* Rename them to be OpenTK.NMatrix# (instead of Simd.MatrixFloat#x#).
* Remove the Vector2 and Vector4 variants, we'll use the OpenTK types instead (but we'll keep the NVector3 variant, since it's not identical to the OpenTK version).
* Update the API to match their OpenTK counterparts better:
* NMatrix2 and NMatrix3 have a 0-based R#C# scheme for their fields.
* NMatrix4 has a 1-based M## scheme for its fields (i.e. no change).
Generate trampoline and registrar tests that tests if a return type requires objc_msgSend or objc_msgSend_stret.
Now it's much easier to test new return types (a single line of code), which
avoids a _lot_ of copy-pasting, and makes sure all the different variations
are tested properly.
These new tests found several bugs, which are fixed in subsequent commits.
Rolf Bjarne Kvinge