Auto merge of #99476 - dpaoliello:rawdylibvectorcall, r=michaelwoerister

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`).

Author: bors