`max_digits10` is the number of decimal digits that the type _can_
represent, in other words, the number of decimal digits needed to
disambiguate any two floating point numbers when serialized to
a string.
Removed:
* NaN normalization
* INFINITY normalization
* errno normalization
* Completely unused duration regex
Tests using these macros should be tagged `[approvals]`
so they are not run as part of approval tests.
Also simplified regex for the test's executable filename,
and hidden some tests relying on nullptr normalization.
