[clang] [HLSL][Matrix] Add support for Matrix element and trunc Casts (PR #168915)

[Farzon Lotfi via cfe-commits]

farzonl wrote:

> Oh, something else missing from this change is that implicit truncations should produce a diagnostic just like we do for vector truncations.

Will address this tomorrow. Thanks for catching that.

https://github.com/llvm/llvm-project/pull/168915