Abstract out System.Reflection.Emit.ILGenerator

[buyaa-n]

Contributes to #62956
Fixes #86110

• Abstract out ILGenerator, move into shared library
  • Kept some APIs virtual (when implementations in Mono and CLR are same or close, we can add more)
  • Made some public APIs abstract (mostly when the Mono and CLR implementations are different)

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Issue Details

---

Contributes to #62956
Fixes #86110

• Abstract out ILGenerator, move into shared library
  • Kept some APIs virtual (when implementations in Mono and CLR are same or close, we can add more)
  • Made some public APIs abstract (mostly when the Mono and CLR implementations are different)

Author:	buyaa-n
Assignees:	-
Labels:	area-System.Reflection, new-api-needs-documentation
Milestone:	-

[jkotas]

LGTM otherwise (once the CI is green).

[jkotas]

LGTM otherwise (once the CI is green).

[buyaa-n]

LGTM otherwise (once the CI is green).

Hm, strangely there are tests that accesses private/internal fields/methods of ILGenerator outside of the CoreLib, not sure how to workaround ...

runtime/src/libraries/System.Linq.Expressions/tests/ILReader/DynamicMethodILProvider.cs

Lines 13 to 19 in 78e42f7

	private static readonly FieldInfo s_fiLen = typeof(ILGenerator).GetFieldAssert("m_length");
	private static readonly FieldInfo s_fiStream = typeof(ILGenerator).GetFieldAssert("m_ILStream");
	private static readonly FieldInfo s_fiExceptions = typeof(ILGenerator).GetFieldAssert("m_exceptions");
	private static readonly FieldInfo s_fiExceptionCount = typeof(ILGenerator).GetFieldAssert("m_exceptionCount");
	private static readonly FieldInfo s_fiLocalSignature = typeof(ILGenerator).GetFieldAssert("m_localSignature");
	private static readonly MethodInfo s_miBakeByteArray = typeof(ILGenerator).GetMethodAssert("BakeByteArray");
	private static readonly MethodInfo s_miMaxStackSize = typeof(ILGenerator).GetMethodAssert("GetMaxStackSize");

[jkotas]

Change it to access fields of RuntimeILGenerator:

private static readonly Type s_runtimeILGenerator = Type.GetType("System.Reflection.Emit.RuntimeILGenerator");
private static readonly FieldInfo s_fiLen = s_runtimeILGenerator.GetFieldAssert("m_length");
...

[buyaa-n]

Change it to access fields of RuntimeILGenerator:

Thank you 🙏!