analyzer: handle strlen(INIT_VAL(STRING_REG)) [PR105899]

analyzer: handle strlen(INIT_VAL(STRING_REG)) [PR105899]

gcc/analyzer/ChangeLog:
	PR analyzer/105899
	* region-model.cc (fragment::has_null_terminator): Move STRING_CST
	handling to fragment::string_cst_has_null_terminator; also use it to
	handle INIT_VAL(STRING_REG).
	(fragment::string_cst_has_null_terminator): New, from above.

gcc/testsuite/ChangeLog:
	PR analyzer/105899
	* gcc.dg/analyzer/strcpy-3.c (test_2): New.

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