The module provides the three system load averages. This is an
improvement compared what you can do with the cpu module: cpu
only provides the one minute sample and the state of the cpu module is
derived from the cpu usage which messes up the formating of the load
average. Also, at least on modern Linux systems, the load of a system
takes much more than the cpu utilization into account and it should
therefore live in a separate module.
summary:
-------
This commit adds xdg-desktop-portal support to waybar. If a portal
supporting `org.freedesktop.portal.Settings` exists, then it will be
queried for the current colorscheme. This colorscheme will then be used
to prefer a `style-light.css` or `style-dark.css` over the basic
`style.css`.
technical details:
-----------------
Appearance is provided by several libraries, such as libhandy (mobile)
and libadwaita. However, waybar links to neither of these libraries. As
the amount of code required to communicate with xdg-desktop portal as a
client is rather minimal, I believe doing so is better than linking to
an additional library.
The Gio library for communicating with dbus is rather messy, Instead of
the `Portal` class containing a `Gio::Dbus::Proxy`, it extends it which
simplifies signal handling.
`Portal` then exposes its own signal, which can be listened to by waybar
to update CSS.
For a reference implementation, please see another one of my projects:
https://github.com/4e554c4c/darkman.nvim/blob/main/portal.go
test plan:
---------
If no desktop portal which provides `Settings` exists, then waybar
continues with the log line
```
[2023-09-06 14:14:37.754] [info] Unable to receive desktop appearance: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such interface “org.freedesktop.portal.Settings” on object at path /org/freedesktop/portal/desktop
```
Furthermore, if `style-light.css` or `style-dark.css` do not exist, then
`style.css` will still be searched for.
Waybar has been tested with both light and dark startup. E.g. if the
appearance is dark on startup the log lines
```
[2023-09-06 14:27:45.379] [info] Discovered appearance 'dark'
[2023-09-06 14:27:45.379] [debug] Try expanding: $XDG_CONFIG_HOME/waybar/style-dark.css
[2023-09-06 14:27:45.379] [debug] Found config file: $XDG_CONFIG_HOME/waybar/style-dark.css
[2023-09-06 14:27:45.379] [info] Using CSS file /home/pounce/.config/waybar/style-dark.css
```
will be observed.
If the color then changes to light during the operation of waybar, it
will change css files:
```
[2023-09-06 14:28:17.173] [info] Received new appearance 'dark'
[2023-09-06 14:28:17.173] [debug] Try expanding: $XDG_CONFIG_HOME/waybar/style-light.css
[2023-09-06 14:28:17.173] [debug] Found config file: $XDG_CONFIG_HOME/waybar/style-light.css
[2023-09-06 14:28:17.173] [info] Using CSS file /home/pounce/.config/waybar/style-light.css
```
Finally, tested resetting waybar and toggling style (works, and style is
only changed once).
fixes: Alexays/Waybar#1973
