Refactor file panel to use render components correctly

[sindrets]

I took care of all the necessary refactoring and the render component stuff, as well as overhauling the visuals of the tree. This seems to work quite well now, but I need to do some further testing.

What works:

• File tree listing for both working files and staged files.
• Configuring listing style to be either list or tree.
• Toggling listing style from the file panel.
• Manually collapsing / un-collapsing folders.
• Automatically un-collapse folders when cycling through files with select_next_entry / select_prev_entry.

What remains to be done:

• Documentation
• Git status for folders
• (up for consideration): compacting empty folders to preserve horizontal space.
  • (see the similar feature I implemented in nvim-tree: feat: Option for grouping empty directories nvim-tree/nvim-tree.lua#247)

[farbodsz]

Perfect - thanks so much!