[clang] [Clang][MicrosoftMangle] Implement mangling for ConstantMatrixType (PR #134930)

[Reid Kleckner via cfe-commits]

https://github.com/rnk commented:

I haven't actually directly implemented one of these, but this approach looks like the others. Please add tests. Also, I see that we use llvm-cxxfilt to validate that the mangling comes back the way we expect. Please add some tests with that utility to check the display name.

https://github.com/llvm/llvm-project/pull/134930