[libc++][format] Improves CTAD.

This partly reverts D133535 and enables CTAD for more parts in format.

Reviewed By: ldionne, #libc

Differential Revision: https://reviews.llvm.org/D135292

GitOrigin-RevId: 261b5abf72cf4cdee240b6887efb6a422e744294
15 files changed