Merge editor.occurrencesHighlight and editor.multiDocumentOccurrencesHighlight setting

[jrieken]

Testing #196342

There is two settings which is confusing because what should happen when occurrencesHighlight is off but multiDocumentOccurrencesHighlight is on? A better solution would be to change editor.occurrencesHighlight to accept true | false (as today) and a new value set of "off" | "singleFile" | "acrossFiles" (names to be defined)

[Yoyokrazy]

Currently, word based suggestion settings are defined as follows:

I can quite easily mirror this approach with:

This behave the exact same as before, simply with a more logical setting name and description. In the current approach, with editor.occurrencesHighlight = false and editor.multiDocumentOccurrencesHighlight = true there will be no occurrence highlighting at all.

Effectively, the following two settings json would be equivalent:

• current:

{
    "editor.occurrencesHighlight": false
    "editor.multiDocumentOccurrencesHighlight": true
}

• proposed:

{
    "editor.occurrencesHighlight": false,
    "editor.occurrencesHighlightMode": "multiFile"
}

If that works, then it's an easy merge of #197690, Otherwise I can go forward with the other approach of merging the settings into a single entry with multiple value sets.