[clang] [HLSL][Matrix] Make matrix truncation respect default matrix memory layout (PR #184280)

[Joshua Batista via cfe-commits]

https://github.com/bob80905 approved this pull request.

LGTM. The only nit I could say is adding an assert message for each row / col assert might help in some debugging situations.

https://github.com/llvm/llvm-project/pull/184280