Annotate the rest of the main package (basically just the Java 8 subjects) for nullness.

And move the `@NullMarked` annotation from individual classes up to the package.

Motivation:
- The annotating is about potentially making things nicer for callers (or any future J2KT use?).
- Moving `@NullMarked` to the package is about saving Truth users from [a warning when running Error Prone with `--release 8`](#1320): When `@NullMarked` appears on a _class_, Error Prone processes the entire `NullMarked` class in order to check whether `NullMarked` is `@Inherited`. This leads to `warning: unknown enum constant ElementType.MODULE` because `NullMarked` has `@Target(MODULE, ...)` but `MODULE` isn't available until Java 9. We'll also be fixing this on the Error Prone side, but we might as well work around it on the Truth side, too—and annotate the rest of Truth while we're at it.

(In principle, I should now add `@NullUnmarked` to all of Truth's test classes, since they haven't been annotated. But doing so would have little to no effect in practice unless maybe IntelliJ recognizes `@NullUnmarked` (probably not now?) or we improve our nullness offerings in Error Prone. I'm planning to not bother, but let me know if I'm being overly lazy.)

Note that this CL applies `@Nullable` to some assertion methods' parameters even though those assertions would always fail if the callers passed `null`. This follows a principle that we'd applied (albeit incompletely) in cl/516515683, which showed that such changes avoided producing build errors in existing, working code. The principle is the same as that discussed for `EqualsTester` in cl/578260904.

Fixes #1320

RELNOTES=Annotated the rest of the main package for nullness, and moved the `@NullMarked` annotation from individual classes up to the package to avoid [a warning under `--release 8`](#1320).
PiperOrigin-RevId: 651891918

Author: cpovirk

core/src/main/java/com/google/common/truth/AbstractArraySubject.java

@@ -20,15 +20,13 @@
 import static com.google.common.truth.Fact.simpleFact;
 
 import java.lang.reflect.Array;
-import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
 /**
  * A common supertype for Array subjects, abstracting some common display and error infrastructure.
  *
  * @author Christian Gruber ([email protected])
  */
-@NullMarked
 abstract class AbstractArraySubject extends Subject {
   private final @Nullable Object actual;
 

core/src/main/java/com/google/common/truth/ActualValueInference.java

@@ -33,7 +33,6 @@
 import java.io.InputStream;
 import java.util.ArrayList;
 import java.util.Map.Entry;
-import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 import org.objectweb.asm.ClassReader;
 import org.objectweb.asm.ClassVisitor;
@@ -70,7 +69,6 @@
  */
 @GwtIncompatible
 @J2ktIncompatible
-@NullMarked
 final class ActualValueInference {
   /** <b>Call {@link Platform#inferDescription} rather than calling this directly.</b> */
   static @Nullable String describeActualValue(String className, String methodName, int lineNumber) {

core/src/main/java/com/google/common/truth/AssertionErrorWithFacts.java

@@ -19,15 +19,13 @@
 import static com.google.common.truth.Fact.makeMessage;
 
 import com.google.common.collect.ImmutableList;
-import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
 /**
  * An {@link AssertionError} composed of structured {@link Fact} instances and other string
  * messages.
  */
 @SuppressWarnings("OverrideThrowableToString") // We intentionally hide the class name.
-@NullMarked
 final class AssertionErrorWithFacts extends AssertionError implements ErrorWithFacts {
   private final ImmutableList<Fact> facts;
 

core/src/main/java/com/google/common/truth/BigDecimalSubject.java

@@ -20,15 +20,13 @@
 import static com.google.common.truth.Fact.simpleFact;
 
 import java.math.BigDecimal;
-import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
 /**
  * Propositions for {@link BigDecimal} typed subjects.
  *
  * @author Kurt Alfred Kluever
  */
-@NullMarked
 public final class BigDecimalSubject extends ComparableSubject<BigDecimal> {
   private final @Nullable BigDecimal actual;
 

core/src/main/java/com/google/common/truth/BooleanSubject.java

@@ -17,15 +17,13 @@
 
 import static com.google.common.truth.Fact.simpleFact;
 
-import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
 /**
  * Propositions for boolean subjects.
  *
  * @author Christian Gruber ([email protected])
  */
-@NullMarked
 public final class BooleanSubject extends Subject {
   private final @Nullable Boolean actual;
 

core/src/main/java/com/google/common/truth/ClassSubject.java

@@ -18,15 +18,13 @@
 import static com.google.common.base.Preconditions.checkNotNull;
 
 import com.google.common.annotations.GwtIncompatible;
-import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
 /**
  * Propositions for {@link Class} subjects.
  *
  * @author Kurt Alfred Kluever
  */
-@NullMarked
 @GwtIncompatible("reflection")
 @J2ktIncompatible
 public final class ClassSubject extends Subject {

core/src/main/java/com/google/common/truth/ComparableSubject.java

@@ -18,7 +18,6 @@
 import static com.google.common.base.Preconditions.checkNotNull;
 
 import com.google.common.collect.Range;
-import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
 /**
@@ -27,7 +26,6 @@
  * @author Kurt Alfred Kluever
  * @param <T> the type of the object being tested by this {@code ComparableSubject}
  */
-@NullMarked
 // TODO(b/136040841): Consider further tightening this to the proper `extends Comparable<? super T>`
 public abstract class ComparableSubject<T extends Comparable<?>> extends Subject {
   /**

core/src/main/java/com/google/common/truth/ComparisonFailureWithFacts.java

@@ -21,14 +21,12 @@
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.truth.Platform.PlatformComparisonFailure;
-import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
 /**
  * An {@link AssertionError} (usually a JUnit {@code ComparisonFailure}, but not under GWT) composed
  * of structured {@link Fact} instances and other string messages.
  */
-@NullMarked
 final class ComparisonFailureWithFacts extends PlatformComparisonFailure implements ErrorWithFacts {
   private final ImmutableList<Fact> facts;
 

core/src/main/java/com/google/common/truth/ComparisonFailures.java

@@ -26,7 +26,6 @@
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableList;
-import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
 /**
@@ -43,7 +42,6 @@
  * different implementation under GWT/j2cl, where {@code ComparisonFailure} is also unavailable but
  * we can't just recover from that at runtime.
  */
-@NullMarked
 final class ComparisonFailures {
   static ImmutableList<Fact> makeComparisonFailureFacts(
       ImmutableList<Fact> headFacts,

core/src/main/java/com/google/common/truth/Correspondence.java

@@ -31,7 +31,6 @@
 import com.google.common.collect.ImmutableList;
 import java.util.Arrays;
 import java.util.List;
-import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
 /**
@@ -66,7 +65,6 @@
  *
  * @author Pete Gillin
  */
-@NullMarked
 public abstract class Correspondence<A extends @Nullable Object, E extends @Nullable Object> {
 
   /**