When using switch-windows-all to cycle through windows across all
workspaces, marco was grouping windows by workspace rather than using
a global MRU (most-recently-used) list. This caused several issues:

- Sticky windows appeared multiple times, once per workspace
- Window order was confusing (since they were grouped by workspace number)
- Behavior was different from other window managers

Fixed by collecting all windows, sorting them by recency, then building
the tab list from this global list.

Fixes #286

pass focus to window if it is on another workspace

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

Add Shift+Print keybinding to trigger 'mate-screenshot --area' for
interactive area selection. This gives users a dedicated keybinding for
area screenshots in addition to the existing Print (screen) and
Alt+Print (window) shortcuts.

Fixes mate-desktop/marco#157

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

Adds GNOME3-style dynamic workspace management. Workspaces are created
when no empty ones exist and removed when multiple empty workspaces are
present, maintaining exactly one empty workspace at the end.

Fixes #406

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.