[Matrix] Intrinsic descriptions

This changes the matrix load/store intrinsic definitions to load/store from/to
a pointer, and not from/to a pointer to a vector, as discussed in D83477.

This also includes the recommit of "[Matrix] Tighten LangRef definitions and
Verifier checks" which adds improved language reference descriptions of the
matrix intrinsics and verifier checks.

Differential Revision: https://reviews.llvm.org/D83785