Git FS: needs to emit events when file is gone

[bpasero]

The history listens to file events and removes entries upon delete. We need to send this from git fs when an editor is no longer valid, otherwise these stick around:

[bpasero]

vscode/src/vs/workbench/services/history/browser/history.ts

Line 284 in ff7e302

this.remove(e); // remove from history files that got deleted or moved

[joaomoreno]

@bpasero These files are never gone, an old version of a file always exists... I'm not really sure I can do anything here.

I believe this support should come from the platform: I don't want these resources to show up in these places at all. The same way I can specify that my file system is readonly, there should be more attributes on a file system which let me control how it behaves in the workbench.