Add support for rewriting unsafe methods

[Miista]

We only discovered this because between .NET Framework 4.8 and .NET 6, calling DateTime.UtcNow invokes unsafe code.

The question is now: how to translate this call?

From what I can gather we have only a metadata signature token (32 bit) and we must somehow use that to resolve and call the correct method (as identified by the token).

UPDATE 2024-06-03: The issue with DateTime.UtcNow only manifests if it is invoked without there existing a shim for it. That is, we can shim the method without issues. However, if we do not shim the method, rewriting it fails.

[Miista]

We should probably also decide whether we support:

• extern
• unmanaged
• unchecked
• operator (implicit and explicit) This is handled in Add support for shimming operators #31
• volatile