Long Vector Execution tests preliminary work to merge a minor refactor.

[alsepkow]

This resolves issue #7531. This is a preliminary step to merging in some of the Long Vector Execution tests currently sitting in the staging-sm6.9 branch. There are no functional changes here, but given that this is a refactor I do not want to add the [NFC] tag to the PR title.

• Moves functions used by existing exec tests and incoming long vector tests to a common HlslExecTestUtils.h.
• Updates naming to adhere to LLVM coding standards for newly created files (even though the functions aren't new)
• Move a few other shared functions to files that make more sense than ExecutionTest.cpp.
• TableParameterHandler class moved to its own header/cpp files. No naming updates as nothing else was touched. Can update in a subsequent PR if it is preferred.
• Add the LLVM coding guidelines preferred include guard to HlslTestUtils.h to mitigate redefinition issues exposed by this refactor.
• Updated the D3D shader model 'redefines' in ExecutionTest.cpp as they were also factored out into a common header. constexpr required because they are enum values.
• BigObj added to the cmake file as I was hitting issues locally for this.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[bob80905]

Just a small question, this LGTM