This change primarly adds a new `Open with...` entry to the explorer context menu. To do this however, I had to make a few other changes:

- Add a new explorer context key for availible editors
- Moved the editor select prompt into a new function called `openEditorWith`
- Use `openEditorWith` for the new `open with` explorer command as well as for the `reopen with` command

* wip 2

* use viewlet stubs

* fix layering issue

* fix saveState and contextmenus

* move context menu logic into panecomposite

* revert tasks.json

* tasks again

* add showHeaderInTitleWhenSingleView values

* patch tests

* some cleanup

* more cleanup

* start view

* merging conflicts

* fix title and dnd

* adding missing api surface to pane composite

* additional merge resolution

fixes #28710

* implement browser clipboard service

* actually register the clipboard service

* update all refs to newly async funcs

* addressing comments

* small fixes

* all asyncs as a result of readText

* fix unit test

* cleanup for writeText refs

* cleanup and reduce diff noise

* qfix

* address feedback