Tracking Issue for LoongArch64 SIMD Intrinsics

This is a tracking issue for the LoongArch64 SIMD Intrinsics.
The feature gate for the issue is #![feature(stdarch_loongarch)].
Parent tracking issue: #117427

Public API

core::arch::loongarch64::lsx_*
core::arch::loongarch64::lasx_*

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.
Discussion comments will get marked as off-topic or deleted.
Repeated discussions on the tracking issue may lead to the tracking issue getting locked.

Steps

• Implement the RFC (cc @rust-lang/XXX -- can anyone write up mentoring
  instructions?)
• Adjust documentation (see instructions on rustc-dev-guide)
• Style updates for any new syntax (nightly-style-procedure)
  • Style team decision on new formatting
  • Formatting for new syntax has been added to the Style Guide
  • (non-blocking) Formatting has been implemented in rustfmt
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

• list all the "unresolved questions" found in the RFC to ensure they are
  not forgotten.

Implementation history

• https://github.com/rust-lang/stdarch/pull/1535
• https://github.com/rust-lang/stdarch/pull/1553
• https://github.com/rust-lang/stdarch/pull/1879
• https://github.com/rust-lang/stdarch/pull/2017

Start with the LoongArch64 public API entries and the linked stdarch pull requests (#1535, #1553, #1879, and #2017), using the feature gate stdarch_loongarch as the entry point. Done means the implementation, documentation, style work, and stabilization checklist items are completed.