[5.1] Implement SE-0251 (#23940)

* Some cleanup of SIMDVector and SIMDVectorTypes source files. (#23389)

Bring formatting closer in line with the rest of the standard lib, remove "public" from extensions (moving it onto the contents defined therein). Restore Swift project headers that were apparently lost at some point.

* [SE-0251] Additions to SIMD types. (#23421)

* Additions to SIMD types.

- extension from 2 and 3-element vectors to 3- and 4-element vectors.
- the .one member
- swizzles via subscript-by-simd
- min/max/sum reductions
- min/max/clamp on vectors-of-comparable
- any and all

- Make permute subscript wrap on vector length, even for SIMD3 dictionaries. Also restore min/max to globals, rather than static functions.

* Temporarily remove the global min(a,b) and max(a,b) SIMD functions. (#23960)

These are triggering a bad compile-time regression for some expressions; that's a bug that should be fixed, but we don't know how to fix it yet, so we'll need to remove these in the short-term, and possibly spell them differently in the medium term.

Author: stephentyrone