Enable source-build with arcade

This enables 'source-build', which makes it easier to build the entire
shipping .NET SDK from source.

This is the first and second step of arcade-powered-source-build:
https://github.com/dotnet/source-build/blob/master/Documentation/planning/arcade-powered-source-build/README.md

See dotnet/sourcelink#692 for a similar PR, that this is based on.

Aside from arcade-specific changes, it also makes all `.sh` files
executable to make this build under Linux/macOS.

The rename from LICENSE to LICENSE.txt is a workaround for
NuGet/Home#7601.

Author: omajid

LICENSE renamed to LICENSE.txt

@@ -24,6 +24,7 @@ stages:
       enablePublishTestResults: true
       enablePublishBuildAssets: true
       enablePublishUsingPipelines: $(_PublishUsingPipelines)
+      enableSourceBuild: true
       enableTelemetry: true
       helixRepo: dotnet/test-templates
       jobs:

azure-pipelines.yml

@@ -0,0 +1,23 @@
+<Project>
+
+  <PropertyGroup>
+    <GitHubRepositoryName>test-templates</GitHubRepositoryName>
+    <SourceBuildManagedOnly>true</SourceBuildManagedOnly>
+  </PropertyGroup>
+
+  <Target Name="ApplySourceBuildPatchFiles"
+          Condition="
+            '$(ArcadeBuildFromSource)' == 'true'"
+          AfterTargets="PrepareInnerSourceBuildRepoRoot">
+
+    <ItemGroup>
+      <SourceBuildPatchFile Include="$(RepositoryEngineeringDir)source-build-patches\*.patch" />
+    </ItemGroup>
+
+    <Exec
+      Command="git apply --ignore-whitespace --whitespace=nowarn &quot;%(SourceBuildPatchFile.FullPath)&quot;"
+      WorkingDirectory="$(CurrentRepoSourceBuildSourceDir)"
+      Condition="'@(SourceBuildPatchFile)' != ''" />
+  </Target>
+
+</Project>

build.sh

@@ -0,0 +1,5 @@
+<UsageData>
+  <IgnorePatterns>
+    <UsagePattern IdentityGlob="*/*" />
+  </IgnorePatterns>
+</UsageData>