fortran: array descriptor: Move array growth function [PR122521]

Move gfc_grow_array, a descriptor growth function used in array constructor
descriptors initialisation, to trans-descriptor.cc.

	PR fortran/122521

gcc/fortran/ChangeLog:

	* trans-array.cc (gfc_grow_array): Move function ...
	* trans-descriptor.cc (gfc_grow_array): ... to this file.
	* trans-descriptor.h (gfc_grow_array): Add declaration.