[release/9.0-staging] Fix getting resource when ResourceResolve returns assembly with resource that is an assembly ref

[elinor-fung]

Backport of #112810
Fixes #111537

Customer Impact

• Customer reported
• Found internally

[Select one or both of the boxes. Describe how this issue impacts customers, citing the expected and actual behaviors and scope of the issue. If customer-reported, provide the issue number.]

Reported in #111537 - Stack overflow on resolving a resource via ResourceResolve for an assembly with an assembly ref manifest resource.

When getting a resource where ResourceResolve handler returns an assembly with a manifest resource that is an assembly ref, we incorrectly resolved the reference on the original assembly instead of the assembly returned by the handler and then also looked for the resource on the original assembly again instead of using the referenced assembly.

Regression

• Yes
• No

Regression in .NET 9 from eae1542.

Testing

Added automated test for manifest resource assembly ref. The manifest resource file (as opposed to assembly ref) case is already covered in libraries tests.

Risk

Low.

Copilot reviewed 1 out of 6 changed files in this pull request and generated no comments.

Files not reviewed (5)

• src/coreclr/vm/peassembly.cpp: Language not supported
• src/tests/Loader/ResourceResolve/ManifestResourceAssemblyRef.il: Language not supported
• src/tests/Loader/ResourceResolve/ManifestResourceAssemblyRef.ilproj: Language not supported
• src/tests/Loader/ResourceResolve/ResourceAssembly.csproj: Language not supported
• src/tests/Loader/ResourceResolve/ResourceResolve.csproj: Language not supported

Comments suppressed due to low confidence (2)

src/tests/Loader/ResourceResolve/ResourceResolve.cs:41

• [nitpick] The variable name 'expectedBytes' is ambiguous. It should be renamed to 'expectedResourceBytes' to better reflect its purpose.

Span<byte> expectedBytes = new byte[expected.Length];

src/tests/Loader/ResourceResolve/ResourceResolve.cs:43

• [nitpick] The variable name 'streamBytes' is ambiguous. It should be renamed to 'actualResourceBytes' to better reflect its purpose.

Span<byte> streamBytes = new byte[stream.Length];