analyzer: remove offset_region size overloads [PR111266]

PR analyzer/111266 reports a missing -Wanalyzer-out-of-bounds when
accessing relative to a concrete byte offset.

Root cause is that offset_region::get_{byte,bit}_size_sval were
attempting to compute the size that's valid to access, rather than the
size of the access attempt.

Fixed by removing these vfunc overrides from offset_region as the
base class implementation does the right thing.

gcc/analyzer/ChangeLog:
	PR analyzer/111266
	* region.cc (offset_region::get_byte_size_sval): Delete.
	(offset_region::get_bit_size_sval): Delete.
	* region.h (region::get_byte_size): Add comment clarifying that
	this relates to the size of the access, rather than the size
	that's valid to access.
	(region::get_bit_size): Likewise.
	(region::get_byte_size_sval): Likewise.
	(region::get_bit_size_sval): Likewise.
	(offset_region::get_byte_size_sval): Delete.
	(offset_region::get_bit_size_sval): Delete.

gcc/testsuite/ChangeLog:
	PR analyzer/111266
	* c-c++-common/analyzer/out-of-bounds-pr111266.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>