[Matrix] Implement C-style explicit type conversions for matrix types.

This implements C-style type conversions for matrix types, as specified
in clang/docs/MatrixTypes.rst.

Fixes PR47141.

Reviewed By: fhahn

Differential Revision: https://reviews.llvm.org/D99037

GitOrigin-RevId: 71ab6c98a0d1b5590ed12f955dea6dfc714e9490
18 files changed