Don't use field digits to format float/Decimal in domain_parser

The conversion of a domain into string should keep the same significant digit,
which means to not use the field digits definition but significant digit of the
value.

issue3266
review1041002
(transplanted from add046625334e0237bc6fc9d684427e6de1b1903)

--HG--
extra : transplant_source : %AD%D0FbS4%E0%23%7B%C6%FC%9DhD%27%E6%DE%1B%19%03