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

For #94408

Moves this out of custom editors

For #94408

fixes #85057

#48258

This reverts commit 85f587ab.

fixes microsoft/vscode-remote-release#1584

fixes #48258