Fix ILLink analyzer assertion for delegates with default parameters

[Copilot]

Description

The ILLink Roslyn analyzer's dataflow analysis hits a Debug.Assert (crash in CI) when encountering a delegate type with a default parameter value, e.g.:

delegate ParallelQuery<int> Operation(int start, int count, Operation source = null);

Roslyn generates an operation block for the default parameter initializer whose OwningSymbol is the delegate's INamedTypeSymbol, not an IMethodSymbol/IFieldSymbol/IPropertySymbol as the analyzer expects.

Fix: Skip interprocedural dataflow analysis in LocalDataFlowAnalysis.InterproceduralAnalyze() when the owning symbol is a delegate type (INamedTypeSymbol { TypeKind: TypeKind.Delegate }). These operation blocks contain only simple constant initializers with no interesting dataflow for trim analysis.

Test: Added a delegate void DelegateWithDefaultParameter(Type type = null) to the existing DelegateCreation test class in AnnotatedMembersAccessedViaReflection.cs.

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[Copilot]

Pull request overview

Fixes a Roslyn ILLink analyzer debug assertion triggered by delegate types that declare optional (defaulted) parameters, where Roslyn reports an operation block whose OwningSymbol is the delegate INamedTypeSymbol instead of a method/field/property symbol.

Changes:

• Skip LocalDataFlowAnalysis.InterproceduralAnalyze() for operation blocks owned by delegate types (INamedTypeSymbol { TypeKind: Delegate }) to avoid constructing MethodBodyValue with an unsupported symbol kind.
• Add a regression test case by introducing a delegate with an optional parameter into an existing dataflow test class.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/tools/illink/src/ILLink.RoslynAnalyzer/DataFlow/LocalDataFlowAnalysis.cs	Early-exits interprocedural analysis when Roslyn provides a delegate-type owning symbol for optional-parameter initializer blocks.
src/tools/illink/test/Mono.Linker.Tests.Cases/DataFlow/AnnotatedMembersAccessedViaReflection.cs	Adds a delegate-with-default-parameter declaration to exercise the analyzer path that previously asserted.

[MichalStrehovsky]

/ba-g wasm timeout