Use the main VT parser in pending mode as well

Should get much closer semantics in the two cases and its nice not to
have an extra mini VT parser for pending mode. There is a performance
hit in pending mode, since now the pending mode bytes are round tripped
via utf-8 decoding/encoding, but its worth it for the code
simplification.

kitty/screen.h

@@ -116,11 +116,9 @@ typedef struct {
     CursorRenderInfo cursor_render_info;
 
     struct {
-        size_t capacity, used, stop_buf_pos;
+        size_t capacity, used;
         uint8_t *buf;
         monotonic_t activated_at, wait_time;
-        int state;
-        uint8_t stop_buf[32];
     } pending_mode;
     DisableLigature disable_ligatures;
     PyObject *marker;