window: Only deny focus if mostly overlapped with always-on-top window

Having an always-on-top window affects focus granting logic if the
to be showing window overlaps with any of them. Instead of triggering
the focus denying logic if a new window ever so slightly touches an
always-on-top window to only triggering if it's covered more than 60% by
always-on-top windows.

This is intended to make using always-on-top windows a bit less annoying
and not cause as many unintended focus-on-map denials.

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

src/tests/meson.build

@@ -727,6 +727,7 @@ stacking_tests = [
   'workspace-test',
   'always-on-top',
   'always-on-top-map-new-maximized',
+  'always-on-top-map-new-partial',
   'focus-default-window-globally-active-input',
   'workspace-unmanaging-window',
   'click-to-focus-and-raise',

src/tests/stacking/always-on-top-map-new-partial.metatest

@@ -0,0 +1,59 @@
+resize_monitor default 400 400
+set_pref center-new-windows true
+
+new_client w wayland
+create w/1 csd
+resize w/1 100 100
+show w/1
+
+assert_focused w/1
+assert_stacking w/1
+
+create w/2 csd
+resize w/2 100 100
+show w/2
+
+assert_focused w/2
+assert_stacking w/1 w/2
+
+create w/3 csd
+resize w/3 100 100
+show w/3
+
+assert_focused w/3
+assert_stacking w/1 w/2 w/3
+
+# Mark two windows as always-above
+
+make_above w/1 true
+move w/1 201 150
+assert_stacking w/2 w/3 w/1
+
+make_above w/3 true
+move w/3 0 0
+assert_stacking w/2 w/1 w/3
+
+# Map another window while the other non-aways-on-top window has focus.
+# It will be mostly visible, so will take focus.
+
+local_activate w/2
+assert_focused w/2
+
+create w/4 csd
+resize w/4 100 100
+show w/4
+
+assert_focused w/4
+assert_stacking w/2 w/4 w/1 w/3
+
+# Move one of the always-on-top window so that the next mapped one will be
+# mostly non-visible, thus not take focus.
+
+move w/1 180 150
+
+create w/5 csd
+resize w/5 100 100
+show w/5
+
+assert_focused w/4
+assert_stacking w/2 w/5 w/4 w/1 w/3