COSMIC Icons Compatibility On macOS

[vkhitrin]

Hi,
I was not able to raise an issue or a discussion at https://github.com/pop-os/freedesktop-icons, so I assume this is the second best place to do so.

Initially I observed issues with icons as part of #763 and #765

Recently, I was able to get COSMIC icons to work on macOS:

(Notice the checkmark in the menu, the delete icon in the search bar, and the close icon in the notification).

Without modifying cosmic-freedesktop-icons or libcosmic I have achieved the following by:

1. Creating a brew Formula https://github.com/vkhitrin/homebrew-tap/blob/main/Formula/cosmic-icons-theme.rb which installs the icons under /opt/homebrew/share/Cosmic).
2. Updating XDG_DATA_DIRS to point to the path above:

    export XDG_DATA_DIRS="/opt/homebrew/share:${XDG_DATA_DIRS}"

I wanted to start a discussion regarding how we could proceed forward with getting icons to work on macOS:

1. Would you approve/encourage distributing cosmic-icons via macOS package mangers (similar to how it is distributed for various Linux package managers)?
2. We should not be setting $XDG_DATA_DIRS on macOS.
   Assuming cosmic-icons will be distributed, would you be willing to add some additional lookup paths for macOS?
3. Which kind of paths should be encouraged to store the icons?
   Other icon themes on macOS (https://formulae.brew.sh/formula/adwaita-icon-theme, https://formulae.brew.sh/formula/hicolor-icon-theme) also create symlinks at /opt/homebrew/share/icons.

EDIT 1:
After compiling the application, and launching it from outside the terminal, XDG_DATA_DIRS were not inherited.
It is possible to set the environment variable to be inherited by GUI applications by launching a LaunchAgent:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
    <dict>
        <key>Label</key>
        <string>setenv.XDG_DATA_DIRS</string>
        <key>ProgramArguments</key>
        <array>
            <string>sh</string>
            <string>-c</string>
            <string>launchctl setenv XDG_DATA_DIRS /opt/homebrew/share</string>
        </array>
        <key>RunAtLoad</key>
        <true />
        <key>KeepAlive</key>
        <true />
    </dict>
</plist>

EDIT 2:
A slightly streamlined LaunchAgent (which is being used by my custom homebrew cask https://github.com/vkhitrin/homebrew-tap/blob/main/Casks/cosmicding.rb):

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.vkhitrin.setenv.XDG_DATA_DIRS</string>
    <key>ProgramArguments</key>
    <array>
        <string>launchctl</string>
        <string>setenv</string>
        <string>XDG_DATA_DIRS</string>
        <string>/opt/homebrew/share</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
</dict>
</plist>