Corner-tiled windows were being treated as maximized horizontally, which
is wrong. Instead, we clear all maximized flags to make sure their size
is respected on reload.

Fixes #710

This prevents race conditions with applications like mate-screenshot
that need to grab input (e.g. for area selection).

Fixes mate-desktop/mate-utils#37

Replace putenv-based child setup with glib environment functions. This
enables posix_spawn for keybindings and it fixes an old memory leak with
not being able to free the string we added to putenv.

There was a 10px difference in the calculation between the (correct)
center-new-windows placement and the (incorrect) move-to-center
keybinding. By using the same function in both places we can make sure
the calculation is consistent.

Extend MetaFrameBorders to include shadow and resize borders to
calculate invisible border size. Also added border caching to prevent
recalculating borders on every frame operation.

This is a backport of the following commits from Metacity:
- https://gitlab.gnome.org/GNOME/metacity/-/commit/21e664af
- https://gitlab.gnome.org/GNOME/metacity/-/commit/3c6e269b
- https://gitlab.gnome.org/GNOME/metacity/-/commit/700e87ea

This allows marco to respond to HiDPI scale changes without requiring
a restart. When the scale changes, marco now automatically updates all
icons (windows, xprops, alt+tab, etc.) and mouse cursor to be at the
correct scale factor.

Window decorations are handled through an internal GDK signal triggered
from XSettings changes, and so already work out of the box.

When calculating the clickable area on the left-most button of
a maximized window, we need to take into account the layout components,
not just the button size.

Fixes mate-desktop/mate-themes#318

Apply Fitt's law to corner window buttons by extending the clickable
area all the way to the edge of the screen on maximized/tiled windows.
This means that a user moving the pointer all the way to the top-right
corner and clicking, will close the maximized (or right-tiled) window.
The same applies for top-left on maximized and left-tiled windows.

Bumps [actions/cache](https://github.com/actions/cache) from 3 to 4.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](https://github.com/actions/cache/compare/v3...v4)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-version: '4'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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