[Wasm Ryujit] codegen for NOT and NEG

[AndyAyersMS]

Wasm has a few wrinkles here to sort through. There is no NOT or NEG for integer types in Wasm.

Also, support returning TYP_LONG directly.

[AndyAyersMS]

@dotgnet/jit PTAL

[AndyAyersMS]

Might want to remove GT_LONG entirely from wasm builds.

[Copilot]

Pull request overview

This PR adds WASM support for NOT and NEG operations in the RyuJIT compiler. Since WASM lacks native NOT and NEG instructions for integer types, the implementation transforms integer NEG operations into SUB(0, x) during lowering, handles NOT using XOR with -1 during code generation, and preserves native f32.neg/f64.neg for floating-point types. Additionally, the PR enables direct TYP_LONG return values for WASM (which has native 64-bit support).

Key Changes

• Added LowerNeg in lowerwasm.cpp to transform integer NEG operations to SUB(0, x)
• Added genCodeForNegNot in codegenwasm.cpp to handle NOT (via XOR with -1) and floating-point NEG
• Modified ContainCheckRet to allow WASM to return TYP_LONG directly without containing GT_LONG nodes

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/coreclr/jit/lowerwasm.cpp	Implements LowerNeg to transform integer NEG operations to SUB(0, x) since WASM lacks native integer NEG
src/coreclr/jit/lower.h	Declares LowerNeg function under TARGET_WASM guard
src/coreclr/jit/lower.cpp	Integrates LowerNeg into LowerNode for GT_NEG case and allows WASM to return TYP_LONG directly
src/coreclr/jit/codegenwasm.cpp	Implements genCodeForNegNot to generate WASM instructions: XOR with -1 for NOT, native f32.neg/f64.neg for floating-point NEG

[SingleAccretion]

LGTM with minor comments.

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