[Feature Request] Add a Shorter Panel Option than XS

[PoisonFrog]

COSMIC has five panel sizes: XS (shortest and default), S, M, L, and XL. The issue is that the XS panel is considerably taller than what many Linux and other OS users are already used to. Configurations for 22px, 24px, or 26px are very common for Waybar. I believe Xfce defaults to a 26px panel, and macOS has a 24px panel for monitors without a notch since Big Sur. All of these are much smaller than COSMIC's smallest option.

I understand the decision from the UX team regarding the panel size choices because the provided options work well with applets that have larger icon sizes (App Tray and Minimized Windows applets). However, if you are only using the default panel applets and have no desire to add any of these large icon applets, then the XS panel seems unnecessarily large for those of us already accustomed to smaller panels. I have been using COSMIC for a month now, and I still think the XS panel is too large for me.

I would suggest adding a 24px panel option called "XXS". I think 24px is a good sweet spot because it is right in the middle of 22px and 26px, which are also popular options for panels in Linux compositors/window managers. Additionally, macOS uses a 24px panel, so it will feel very familiar to those coming from macOS. The applet icon size could remain the same as the XS panel (16px) since the tray icons would not need to be smaller. I guess the rest could be adjusted by the UX team if needed.

I think this would be a great change for many users, and I'm confident the "XXS" panel would be a more popular choice than some of the larger options.

[PoisonFrog]

I'll close this since #319 is a much better solution.