Fortran: implement vector sections in DATA statements [PR49588]

gcc/fortran/ChangeLog:

	PR fortran/49588
	* data.cc (gfc_advance_section): Derive next index set and next offset
	into DATA variable also for array references using vector sections.
	Use auxiliary array to keep track of offsets into indexing vectors.
	(gfc_get_section_index): Set up initial indices also for DATA variables
	with array references using vector sections.
	* data.h (gfc_get_section_index): Adjust prototype.
	(gfc_advance_section): Likewise.
	* resolve.cc (check_data_variable): Pass vector offsets.

gcc/testsuite/ChangeLog:

	PR fortran/49588
	* gfortran.dg/data_vector_section.f90: New test.