Implement Vector.Ceiling / Vector.Floor (#31993)

Implement Vector.Ceiling / Vector.Floor (#31993)

* Add Ceil/Floor to S.P.CoreLib and expose publicly

* Make Ceil/Floor JIT intrinsic

* Add missing identifier for closing endif

* Add JIT test for Ceil/Floor

* Add test for Ceil/Floor in S.Numerics.Vectors
* Also fix the old path for the new structure

* Apply jit-format

* Do not attempt to treat Ceil/Floor if SSE4.1 isn't available

* Mark Vector<T>.Ceiling/Floor as Intrinsic

* Add missing underscore

* Revert "Add missing idenfitier for closing endif"
* Oops

* Add missing breaks
* Oops, again

* Simplify switch case

* Per review suggestion

Co-Authored-By: Egor Chesakov <egor.chesakov@microsoft.com>
Co-authored-by: Egor Chesakov <egor.chesakov@microsoft.com>