Multiple Entry Point Cleanup (shader-slang#1427)

* Multiple Entry Point Cleanup

This commit provides some in-code cleanup of the previous multiple entry point PR (shader-slang#1411).  Specifically, this PR provides refactoring of multiple entry point functions into helper functions, the removal of the EntryPointAndIndex struct, and various stylistic improvements.

* Minor updates

Co-authored-by: Tim Foley <tfoleyNV@users.noreply.github.com>

Author: Checkmate50