Auto merge of #117468 - daxpedda:wasm-relaxed-simd, r=alexcrichton

Stabilize Wasm relaxed SIMD

This PR stabilizes [Wasm relaxed SIMD](https://github.com/WebAssembly/relaxed-simd) which has already reached [phase 4](https://github.com/WebAssembly/proposals/tree/04fa8c810e1dc99ab399e41052a6e427ee988180?tab=readme-ov-file#phase-4---standardize-the-feature-wg).

Tracking issue: #111196
Implementation PR: rust-lang/stdarch#1393
Documentation: rust-lang/reference#1421
Stdarch: rust-lang/stdarch#1494

Closes #111196.

Author: bors