[libc++][format] Mark range formaters as complete.

The __cpp_lib_format_ranges feature-test macro only depends on P2286R8
and P2585R0. Note since LWG3750 only affects these two C++23 papers
there is nothing to do for older language versions.

(The __cpp_lib_format feature-test macro depends on the incomplete
formatting for chrono. So this part can't be marked as complete yet.)

This completes
- P2286R8 Formatting ranges
- P2585R0 Improving default container formatting

This partly implements
- LWG3750 Too many papers bump __cpp_lib_format

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D147880