Add new keys for diferent styling of "ui.statusline.separator" depending on editor mode

[0rphee]

It'd be great to have more options for styling "ui.statusline.separator", like there are for the editor mode indicator in order to prevent stuff like this:

There already exists:

"ui.statusline" = {}
"ui.statusline.normal" = {}
"ui.statusline.insert" = {}
"ui.statusline.select" = {}
"ui.statusline.inactive" = {}

I propose to add

"ui.statusline.separator" = {} # already exists
"ui.statusline.separator.normal" = {}
"ui.statusline.separator.insert" = {}
"ui.statusline.separator.select" = {}
"ui.statusline.separator.inactive" = {}

Probably related to: #5022 & #5722

[7ombie]

This is not an enhancement. It should be labeled as a bug, as you cannot use color-modes and a separator at the same time. The separator is not colored correctly, due to an oversight in the design.

There are things that could be done to enhance the related features, but this issue should be addressed first, as it breaks the editor UI when enabled.