Add quirk mode for #35110

Author: AndriySvyryd

src/EFCore/Metadata/Conventions/ForeignKeyPropertyDiscoveryConvention.cs

@@ -50,6 +50,9 @@ public class ForeignKeyPropertyDiscoveryConvention :
     IPropertyFieldChangedConvention,
     IModelFinalizingConvention
 {
+    private static readonly bool UseOldBehavior35110 =
+        AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore.Issue35110", out var enabled) && enabled;
+
     /// <summary>
     ///     Creates a new instance of <see cref="ForeignKeyPropertyDiscoveryConvention" />.
     /// </summary>
@@ -81,7 +84,8 @@ private IConventionForeignKeyBuilder ProcessForeignKey(
         IConventionContext context)
     {
         var shouldBeRequired = true;
-        if (!relationshipBuilder.Metadata.IsOwnership)
+        if (!relationshipBuilder.Metadata.IsOwnership
+            || UseOldBehavior35110)
         {
             foreach (var property in relationshipBuilder.Metadata.Properties)
             {

src/EFCore/Metadata/Internal/InternalEntityTypeBuilder.cs

@@ -15,6 +15,9 @@ namespace Microsoft.EntityFrameworkCore.Metadata.Internal;
 /// </summary>
 public class InternalEntityTypeBuilder : InternalTypeBaseBuilder, IConventionEntityTypeBuilder
 {
+    private static readonly bool UseOldBehavior35110 =
+        AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore.Issue35110", out var enabled) && enabled;
+
     /// <summary>
     ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
     ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
@@ -3171,8 +3174,12 @@ public static InternalIndexBuilder DetachIndex(Index indexToDetach)
                     + "Owned types should only have ownership or ownee navigations point at it");
 
                 relationship = relationship.IsOwnership(true, configurationSource)
-                    ?.HasNavigations(inverse, navigation, configurationSource)
-                    ?.IsRequired(true, configurationSource);
+                    ?.HasNavigations(inverse, navigation, configurationSource);
+
+                if (!UseOldBehavior35110)
+                {
+                    relationship = relationship?.IsRequired(true, configurationSource);
+                }
 
                 relationship?.Metadata.UpdateConfigurationSource(configurationSource);
                 return relationship;