Implement Matrix Get Element Builtin #7900

Create __builtin_LinAlg_MatrixGetElement(MatrixRef, int index) and lower it to dx.op.matrixGetElement as specified in https://github.com/microsoft/hlsl-specs/blob/main/proposals/0035-linalg-matrix.md

Changes required:

• If necessary, update the intrinsic definition in utils/hct/gen_intrin_main.txt
• In lib/HLSL/HLOperationLower.cpp
  • Create a new lowering function TranslateLinAlgMatrixGetElement
  • Update the mapping table for IOP___builtin_LinAlg_MatrixGetElement from EmptyLower to TranslateLinAlgMatrixGetElement
• Write frontend tests in tools/clang/test/SemaHLSL/hlsl/linalg/builtins/matrixgetelement
• Update frontend tests in tools/clang/test/SemaHLSL/hlsl/linalg/builtins
• If necessary, update the opcode definition in utils/hct/hctdb.py (be sure to check allowed stages)
• Update codegen tests in tools/clang/test/CodeGenDXIL/hlsl/linalg/builtins
• For complex ops, write codegen tests in tools/clang/test/CodeGenDXIL/hlsl/linalg/builtins/matrixgetelement

Note: The spec is not final therefore this issue may fall out of date. The spec is the source of truth and should be referenced during implementation.