Feat: Toolbar

[benjamin-kirkbride]

Solves #1332

This is a first pass, looking for feedback.

Please don't get caught up on the current buttons being for black and isort, I am sure you feel that having a dedicated toolbar for these are not of much value, and I agree, but they were the easiest to start with as an example.

I am seeking feedback on how I implemented the toolbar, and how it is interacted with from other plugins. Ideally we come up with a pattern for "registering" "commands" that can be selectively shared between the toolbar, Command Palette, right click menu, and probably the main menu as well?

Features I have thought of, and their status:

• implement as a plugin such that it (I believe) can be completely disabled
• toolbar only appearing for filetypes that it has buttons registered for
• way to control ordering of buttons (needs some more thought maybe)
• better theming/appearance of the toolbar
  • button colors
  • button symbols/images
    • work through the sourcing/svg problem
  • toolbar separators
  • toolbar padding
  • toolbar outline
• user able to disable toolbar on a per-filetype basis

PS I may have gone a bit overboard with the custom classes 😅

[benjamin-kirkbride]

Also, I rebased all my other branches onto this one, that will need worked through at some point but till then focus on 8775d89 - that is where the changes are.

[benjamin-kirkbride]

One thing in particular I would like feedback on is how to test this. The buttons are being generated dynamically, so I'm not sure how to "emulate" clicking them to verify their functionality.