analyzer: fix ICEs treeifying offset_region [PR96646, PR96841]

analyzer: fix ICEs treeifying offset_region [PR96646, PR96841]

gcc/analyzer/ChangeLog:
	PR analyzer/96646
	PR analyzer/96841
	* region-model.cc (region_model::get_representative_path_var):
	When handling offset_region, wrap the MEM_REF's first argument in
	an ADDR_EXPR of pointer type, rather than simply using the tree
	for the parent region.  Require the MEM_REF's second argument to
	be an integer constant.

gcc/testsuite/ChangeLog:
	PR analyzer/96646
	PR analyzer/96841
	* gcc.dg/analyzer/pr96646.c: New test.
	* gcc.dg/analyzer/pr96841.c: New test.