Fix by-ref list assign LIST_W+MAKE_REF separation

Fix by-ref list assign LIST_W+MAKE_REF separation

Shift the responsibility for emitting MAKE_REF to the list assignment
code, to make sure that LIST_W and MAKE_REF are directly adjacent,
and there are no opcodes in between that could modify the LIST_W
result.

Additionally, adjust the zend_wrong_string_offset() code to not
perform a loop over opcodes and assert that the next opcode is
a relevant one. The VM write-safety model requires this.

This is a followup to a07c1f56aac1c0f6c8334760009b678cbf9d6138
and the full fix for oss-fuzz #25352.