Add basic boosts implementation

[FlorianButz]

This PR aims to implement a basic version of the Boosts feature from Arc. This currently features font customization, theme customization and smart inverting.

ScreenRecording_Boosts.mp4

[12th-devs]

I love this so much!

[mr-cheffy]

I've added the boilerplate code we should use in order to change how firefox renders colors for certain shells. If you could make it in a window instead of a popup, it would be great via using Services.obs to communicate. Would also remove the need for ZenBoosts.mjs.

[mr-cheffy]

Very excited for the implementation I came up with!

We edit firefox's rendering engine to "filter" the colors that where going to be displayed on the screen, unlike arc which I believe they use filters on the document. This means our solution is more efficient + more compatible with websites

Example:

And here's where zen's (1) vs arc's (2) implementation really differ:

zen:

arc:

[FlorianButz]

Changed the editor UI to look more like the one from Arc

[12th-devs]

Changed the editor UI to look more like the one from Arc

@FlorianButz a few questions I had:

1. How does it look in dark mode?

2. How is the size controlled? Drop down list, typing, scroll over the container?

3. What is with the right margin on the size percentage

4. Could the button inside of the gradiant picker be tweaked a bit? It feels a bit out of place in my opinion, but I would love to hear your side.

This all looks so good and I'm really excited, great work man!

[FlorianButz]

@12th-devs

1. There is no dark mode. Arc does not have it, so I left it out for the time being. This can still be added later on if necessary.
2. The size changes the zoom on the website, the dropdown list shows all available system fonts, the typing overrides the text case
3. There are still quite a few visual issues. However to not slow down the development I decided to commit the changes now. Perfecting can be done after everything else is in place.
4. As I said in 3, there's still some issues I currently don't want to prioritize

[12th-devs]

@FlorianButz that sounds good, thanks for the quick response.