Add tests for raw-dylib with vectorcall, and fix vectorcall code generation * Adds tests for using `raw-dylib` (#58713) with `vectorcall`. * Fixed code generation for `vectorcall` (parameters have to be marked with `InReg`, just like `fastcall`). * Enabled running the `raw-dylib` `fastcall` tests when using MSVC (since I had to add support in the test for running MSVC-only tests since GCC doesn't support `vectorcall`).