This PR is to add AT edit descriptor, a new feature of Fortran 2023, 5.1
US 10.
AT is like A (character output) but trims trailing blanks before
emitting the string. AT is functionally the same as TRIM intrinsic.
AT is treated as a variant of A during parse. The trimming of the
trailing spaces are implemented the same as TRIM(). There exists a
method, LenTrim, that can be used to do the trimming. However it's local
to a different .cpp file, character.cpp. And the code is so simple that
no need to make extra effort to use LenTrim.
AT is output only and do not accept width.
This PR will fix#181379.
323c3da8dc