[TrimmableTypeMap] Generate ProGuard for types in type map #10790

Part of #10788

Once the list of types that survived trimming is known, we can generate ProGuard rules to specify which ACW/JCW Java classes we want to keep via the -keep class jni.class.Name { *; } rules.

• The build task needs to run after ILLink or ILC and before we run Java trimming (r8).
• This task should run incrementally only when ILLink or ILC produce different typemap.
• This task should not run in Debug at all.

Getting the list of types that are in the typemap might not be trivial at the moment:

• CoreCLR: we can scan the trimmed type map assembly and see which attributes were kept
• Native AOT needs to give us the list of types it kept in the typemap: TypeMap API: For trimmed and nativeaot builds, provide a list of the types kept by the typemap runtime#120204. As a workaround, we can opt into ILC's existing diagnostic outputs ($(IlcGenerateMetadataLog) or $(IlcGenerateDgmlFile)) but these artifacts are quite large and writing them to disk, reading them from disk, and scanning them will add non-trivial time to the overall build.

Ideally, ILLink and ILC will produce some form of list of types which are included in the typemap, which would allow us to implement a unified build task to generate the proguard rules.