[format.formatter.spec]/5 lists the requirements for the default
formatter. The original implementation didn't implement this. This
implements the default formatter according to the Standard.
This adds additional test to validate the default formatter is disabled
and the required standard formatters are enabled.
While adding the tests it seems the formatters needed a constraint for the
character types they were valid for.
Implements parts of:
- P0645 Text Formatting
Depends on D115988
clang-format suggested style edits found: