[RyuJit Wasm] don't home locals if none are referenced

[AndyAyersMS]

In such cases we won't have set up a stack pointer.

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Pull request overview

This PR updates the WASM JIT codegen to avoid homing parameters when no locals or arguments require stack-based storage, i.e., when no stack pointer register has been set up.

Changes:

• Add a guard in CodeGen::genHomeRegisterParams that checks GetStackPointerReg() and skips parameter homing when it is REG_NA.
• Assert that the frame pointer is not used in this frameless case and emit a JITDUMP message for debugging.

[AndyAyersMS]

@dotnet/jit-contrib PTAL
@SingleAccretion let me know if you think we should handle this some other way.

Fixes codegen for methods with no (user) arguments, like

    public static int Zero() => 0;