Implement classMustBeLoadedBeforeCodeIsRun in crossgen2 (#608)

Implement classMustBeLoadedBeforeCodeIsRun in crossgen2 (#608)

* Implement classMustBeLoadedBeforeCodeIsRun in crossgen2

This fixes missing eager fixups for method call arguments and return
value for methods going through PreStub.
It fixes the coreclr JIT\Regression\CLR-x86-JIT\V1.2-M01\b02345\b02345
test that needed Span<byte> type during GC stack walk with PreStub of a
method with Span<byte> argument on the stack and failed as it couldn't
be loaded during the GC.
The same failure also happened in many if not all tests when I have
attempted to run them with GCStress 3.

* Reflect PR feedback on member / property naming and method location