This fixes a major inconsistency with the swaybar implementation of
these modes[^1]. `overlay` layer no longer has security implications due
to a wide adoption of `ext-session-lock`, so it's safe to use.

Following config will restore the previous behavior:
```json
"modes": {
    "hide": { "layer": "top" },
    "overlay": { "layer": "top" }
},
```

[^1]: swaywm/sway@2f7247e

All the mode or visibility changes require `wl_surface_commit` to be
applied. gtk-layer-shell will attempt to force GTK to commit, but may
fail if the surface has stopped receiving frame callbacks[^1].
Thus, we could get stuck in a state where the bar is hidden and unable
to regain visibility.

To address this, a new API has been added to gtk-layer-shell,
`gtk_layer_try_force_commit`, which does `wl_surface_commit` with the
necessary safety checks to avoid corrupting GTK internal state.

Note: this change bumps gtk-layer-shell requirement to 0.9.0.

[^1]: wmww/gtk-layer-shell#185

Previous commit should have a better workaround for Alexays#3211.

This reverts commit b61ea62.

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/71e91c409d1e654808b2621f28a327acfdad8dc2?narHash=sha256-GnR7/ibgIH1vhoy8cYdmXE6iyZqKqFxQSVkFgosBh6w%3D' (2024-08-28)
  → 'github:NixOS/nixpkgs/4f807e8940284ad7925ebd0a0993d2a1791acb2f?narHash=sha256-IiA3jfbR7K/B5%2B9byVi9BZGWTD4VSbWe8VLpp9B/iYk%3D' (2024-09-11)