Restrict open editors to a certain number

[tsmaeder]

Feature Description:

I propose that we introduce a preference to allow for only a certain number of editors (say "20"). When this number is reached, the least recently used editor is closed when a new one is opened.

We currently have the "enablePreview" setting, but that behavior closes the most recently used editor (unless I explicitly prevent that). But when browsing around code, I often want to go back and forth between editors, even though I'm just reading code. My focus for reading code moves to different areas as I go along, so editors from other areas can be closed.

[vince-fugnitto]

A combination of the following preferences in VS Code:

• workbench.editor.limit.enabled
• workbench.editor.limit.value

VS Code provides a few other related preferences to control the behavior further (ex: dirty files, editor groups).