[flang][MIF] Update prif_coarray_handle in accordance with PRIF 0.8 #214080 (#214747)
In PRIF revision 0.8, the representation of `prif_coarray_handle` was
changed. This PR updates this representation for this type and updates
the MIFOpConversion pass for the relevant operations.
Fixes issue #214080
A minor fix has been made to the deallocation to ensure that, on the
Flang side, the variable is properly deallocated, since previously the
deallocation was only performed at the `coarray_handle` level.