Rollup merge of #137828 - folkertdev:simd-intrinsic-doc-fixes, r=workingjubilee

Fix inaccurate `std::intrinsics::simd` documentation

This addresses two issues:

- the docs on comparison operators (`simd_gt` etc.) said they only work for floating-point vectors, but they work for integer vectors too.
- the docs on various functions that use a mask did not document that the mask must be a signed integer vector. Unsigned integer vectors would cause invalid behavior when the mask vector is widened (unsigned integers would use zero extension, producing incorrect results).

r? ``@workingjubilee``

Author: matthiaskrgr