Warning suppressions in compiler generated code (#2075)

This change implements the following high-level functionality:
* `UnconditionalSuppressMessage` applies to the entire method body even for iterators, async methods
* `RequiresUnreferencedCode` automatically suppresses trim analysis warnings from entire method body for iterators, async methods

Solution approach:
* Detect compiler generated code by using the `IteratorStateMachineAttribute`, `AsyncStateMachineAttribute` and `AyncIteratorStateMachineAttribute`.
  * When a method which is compiler generated (detected by looing for `<` in its name) is processed the original "user method" is determined by looking for a method with the "state machine" attribute pointing to the compiler generated type.
  * This information is cached to avoid duplication of relatively expensive detection logic.
* Looks for `UnconditionalSuppressMessage` and `RequriesUnreferencedCode` in:
  * If the warning origin is not a compiler generated code - simply use the warning origin (method) - existing behavior
  * If the warning origin is compiler generated use both the origin as well as the user defined method (non-compiler-generated) which is the source of the code for the compiler generated origin

This is done by storing additional `SuppressionContextMember` on `MessageOrigin` which should always point to non-compiler-generated item.

Added lot of new tests for these scenarios.

This implements warning suppression part of https://github.com/mono/linker/issues/2001 for state machines.

1 files changed, 2 insertions, 0 deletions

diff --git a/test/Mono.Linker.Tests.Cases.Expectations/Assertions/ExpectedWarningAttribute.cs b/test/Mono.Linker.Tests.Cases.Expectations/Assertions/ExpectedWarningAttribute.cs
index 85bd85d67..04ba3fdcb 100644
--- a/test/Mono.Linker.Tests.Cases.Expectations/Assertions/ExpectedWarningAttribute.cs
+++ b/test/Mono.Linker.Tests.Cases.Expectations/Assertions/ExpectedWarningAttribute.cs
@@ -18,5 +18,7 @@ namespace Mono.Linker.Tests.Cases.Expectations.Assertions
 
 		// Set to true if the warning only applies to global analysis (ILLinker, as opposed to Roslyn Analyzer)
 		public bool GlobalAnalysisOnly { get; set; }
+
+		public bool CompilerGeneratedCode { get; set; }
 	}
 }