[HLSL][Vulkan] Correctly validate static constraints around entrypoints

HLSL/Vulkan has a few restrictions like:
- there can be only one push constant statically used per entry point
- there can be no static recursion

Current Sema is not handling those.

Start in Sema, tracing how HLSL/Vulkan entry points are analyzed and where static resource use and recursion are represented. Add coverage for the one-push-constant and no-static-recursion restrictions, then verify the relevant compiler tests reject invalid cases.

Written by the indexing model from the issue text.