Fuzzy File Opener widget uses existing workspace data

[robobenklein]

Same functions as Atom implementation.

[robobenklein]

Related / potential re-usable: https://eclipse-theia.github.io/theia/docs/next/modules/search_in_workspace.html

[robobenklein]

monaco init changed:
https://github.com/eclipse-theia/theia/blob/release/1.47.x/CHANGELOG.md#breaking_changes_1.47.0

[robobenklein]

needed in general to hold focus, otherwise focus (activations) can't be moved along the ribbon past empty patches unless there's something like this to hold / take said focus when an empty patch is activated