[libc++][chrono] Add hh_mm_ss formatter.

Partially implements:
- P1361 Integration of chrono with text formatting
- P2372 Fixing locale handling in chrono formatters
- P1466 Miscellaneous minor fixes for chrono

Depends on D137022

Reviewed By: ldionne, #libc

Differential Revision: https://reviews.llvm.org/D139771