[VFABI] Improve VFABI unit tests (#73907)

The below changes were made:
- test the vector and scalar names, the ISA, and the presence or absence of a
  mask in all tests that is relevant
- test the number of the parameters, the order/types and for masks if present
- replaced methods like `sin` to `foo` to make it more clear that these are not
  existing functions but they are rather tests.
- using mostly `i32` for parameters where it is not relevant, except when the VF
  of elements in explicitly checked, and `ptr` for references.
  Also using `void` for return types.
- all `VFABIParserTest` tests are now listed contiguously in the source.
- Removed duplicate ISA tests
- Added an extra test to clearly show that the mangled name becomes the
  VectorName, when no VectorName is specified.
- Use `VFInfo` for `isMasked`
- Minor code refactoring, cleanup, and improved comments

Author: paschalis-mpeis