Expose quick-open functionality

For a project I am working on I would love to use the QuickOpen functionality of the monaco editor for custom command-lists (or selection, ...) after executing another command.

An example for what I mean could be the "Go To Line" command, wich opens a new QuickOpen View and after executing shows a single command which jumps to the given line.

I imagine adding custom actions like "Rename file..." (action outside of monaco) or "Switch Language Mode...".

I tried to get the responsible controller and show it, but i didn't get it to work, because of exceptions about the object properties of QuickOpenModel (just giving an array does not work).
I got it to work by extending IActionDescriptor by getQuickOpenEntries() (this or run() is required in the addAction method of StandaloneCodeEditor, which does the magic). What I didn't get to work here was a usable build from my custom-code (like npm-folder with dev, min, ...).

If this is appreciated by others, maybe we could get this to work for everyone.

Start with StandaloneCodeEditor.addAction, IActionDescriptor, and QuickOpenModel, since the issue identifies these as the relevant entry points. Clarify how custom actions should provide QuickOpen entries and how the public build should expose them. Done should mean a documented, usable way to open custom command lists or selections after another command.