[mobile] Fix IL2007 in System.Runtime.Loader.Tests on non-iOS apple-mobile targets

[kotlarmilos]

Note

This PR description was drafted with assistance from GitHub Copilot.

Description

Fixes IL2007 build failure in System.Runtime.Loader.Tests on every Apple-mobile target except iOS/tvOS device:

src/libraries/System.Runtime.Loader/tests/ILLink.Descriptors.xml(5,4):
  error IL2007: Could not resolve assembly 'System.Runtime.Loader.Test.Assembly'.
src/libraries/System.Runtime.Loader/tests/ILLink.Descriptors.xml(6,4):
  error IL2007: Could not resolve assembly 'System.Runtime.Loader.Test.Assembly2'.

Reproduces in runtime-extra-platforms legs Build maccatalyst-arm64 Release AllSubsets_CoreCLR, maccatalyst-x64 Release AllSubsets_CoreCLR, iossimulator-arm64/x64 Release AllSubsets_CoreCLR, tvos-arm64 Release AllSubsets_CoreCLR_RuntimeTests. First reproduction on main: build 1403076 (commit 8f854afd60, Apr 30); the build immediately before — 1401195 (9a6034a3ea) — was clean.

Cause

#127058 added two <assembly> entries to the shared ILLink.Descriptors.xml:

<assembly fullname="System.Runtime.Loader.Test.Assembly" />
<assembly fullname="System.Runtime.Loader.Test.Assembly2" />

But the corresponding ProjectReference in System.Runtime.Loader.Tests.csproj only deploys those two assemblies as separate files on iOS/tvOS:

<ProjectReference Condition="'$(TargetOS)' != 'ios' and '$(TargetOS)' != 'tvos'"
                  Include="System.Runtime.Loader.Test.Assembly\..."
                  ReferenceOutputAssembly="false" OutputItemType="EmbeddedResource" />
<ProjectReference Condition="'$(TargetOS)' == 'ios' or '$(TargetOS)' == 'tvos'"
                  Include="System.Runtime.Loader.Test.Assembly\..." />

On every other platform they are embedded resources, so ILLink can't resolve them as standalone assemblies and fails with IL2007 whenever the descriptor is included (i.e. with aggressive trimming).

Fix

Split the two iOS/tvOS-only entries into a sibling ILLink.Descriptors.AppleDevice.xml and <TrimmerRootDescriptor> it only on (TargetOS == 'ios' or TargetOS == 'tvos') && EnableAggressiveTrimming && !UseNativeAotRuntime.

[Copilot]

Pull request overview

Fixes IL2007 build errors in System.Runtime.Loader.Tests on Apple-mobile targets other than iOS/tvOS device (Mac Catalyst, iOS simulator, tvOS simulator) introduced by #127058. The shared ILLink.Descriptors.xml referenced System.Runtime.Loader.Test.Assembly{,2} as standalone assemblies, but those projects are only deployed as separate files on iOS/tvOS — elsewhere they are embedded resources, so ILLink cannot resolve them.

Changes:

• Remove the two iOS/tvOS-only entries from the shared ILLink.Descriptors.xml.
• Add a new ILLink.Descriptors.AppleDevice.xml containing those two entries.
• Reference the new descriptor from the csproj only on (ios|tvos) && EnableAggressiveTrimming && !UseNativeAotRuntime, matching the ProjectReference deployment conditions.

Show a summary per file

File	Description
src/libraries/System.Runtime.Loader/tests/ILLink.Descriptors.xml	Removes the two iOS/tvOS-only assembly entries that caused IL2007 elsewhere.
src/libraries/System.Runtime.Loader/tests/ILLink.Descriptors.AppleDevice.xml	New descriptor file preserving the two test assemblies under aggressive trimming on iOS/tvOS.
src/libraries/System.Runtime.Loader/tests/System.Runtime.Loader.Tests.csproj	Conditionally includes the new descriptor for iOS/tvOS with aggressive trimming (non-NativeAOT).

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 0