window: Add place flags

Replace a boolean argument and a temporary MetaWindow struct field with
a `MetaPlaceFlag` passed where relevant. This includes
`meta_window_move_resize_internal()` and `meta_window_constrain()`, as
placement may happen during constraining, and also
`meta_window_force_placement()`.

The struct field (denied_focus_and_not_transient) was only ever set in
meta_window_show(), before meta_window_force_placement(), and
immediately unset as a side effect of that. In .._show() we'll always
force placement if the window wasn't already placed, and in
meta_window_constrain(), we'd only ever call meta_window_place() if the
window wasn't already placed, meaning the variable would only ever be
relevant during `meta_window_show()`. Having it as a flag makes that
relationship and temporary state clearer.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3879>

src/core/constraints.h

@@ -27,6 +27,7 @@
 
 void meta_window_constrain (MetaWindow          *window,
                             MetaMoveResizeFlags  flags,
+                            MetaPlaceFlag        place_flags,
                             MetaGravity          resize_gravity,
                             const MtkRectangle  *orig,
                             MtkRectangle        *new,