analyzer: reimplement kf_strcpy [PR105899]

analyzer: reimplement kf_strcpy [PR105899]

This patch reimplements the analyzer's implementation of strcpy using
the region_model::scan_for_null_terminator infrastructure, so that e.g.
it can complain about out-of-bounds reads/writes, unterminated strings,
etc.

gcc/analyzer/ChangeLog:
	PR analyzer/105899
	* kf.cc (kf_strcpy::impl_call_pre): Reimplement using
	check_for_null_terminated_string_arg.
	* region-model.cc (region_model::get_store_bytes): Shortcut
	reading all of a string_region.
	(region_model::scan_for_null_terminator): Use get_store_value for
	the bytes rather than "unknown" when returning an unknown length.
	(region_model::write_bytes): New.
	* region-model.h (region_model::write_bytes): New decl.

gcc/testsuite/ChangeLog:
	PR analyzer/105899
	* gcc.dg/analyzer/out-of-bounds-diagram-16.c: New test.
	* gcc.dg/analyzer/strcpy-1.c: Add test coverage.
	* gcc.dg/analyzer/strcpy-3.c: Likewise.
	* gcc.dg/analyzer/strcpy-4.c: New test.

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