Pick a forever theme color for the quick fix highlight and allow styling both background and borders

[Tyriar]

Testing #194072

We cover bg and border for the majority of highlights, for example:

		"editor.lineHighlightBorder": "#263040",
		"editor.rangeHighlightBackground": "#ffffff0d",
		"editor.selectionBackground": "#399ef440",
		"editor.selectionHighlightBackground": "#399ef420",
		"editor.wordHighlightBackground": "#00000000",
		"editor.wordHighlightBorder": "#399ef4",
		"editor.wordHighlightStrongBackground": "#00000000",
		"editor.wordHighlightStrongBorder": "#399ef4",

We should look into whether one of those is suitable and use that, or make our own and choose a good base to derive from. Provided there's no conflicts, I'll likely make my theme use the bright accent border I use for word highlight:

We want to make sure that it behaves correctly when there is for example find in files, find in the current file, etc. already active.

[justschen]

example here (since i'm using 'editor.findMatchHighlightBackground` with no changes):

[justschen]

will be addressed as part of #199608

[Tyriar]

@justschen that looks like it's more API related, you sure you want to combine them as this ask could get lost? Smaller scoped issues are always easier to deal with imo.