Introduce float4in_internal
This is the guts of float4in, callable as a routine to input floats,
which will be useful in an upcoming patch for allowing soft errors in
the seg module's input function.
A similar operation was performed some years ago for float8in in
commit
50861cd683e.
Reviewed by Tom Lane
Discussion: https://postgr.es/m/
cee4e426-d014-c0b7-aa22-
a659f2cd9130@dunslane.net