Accept multiple URIs for the open file command

[vinistock]

Motivation

This PR starts accepting a list of URIs for the open file command. This will be necessary for allowing the jump to view feature to exist, since applications may define multiple views for the same controller action with different formats (e.g.: index.html.erb, index.json.jbuilder).

Implementation

The idea is to accept full URIs from the server. If there's only one, we open that directly. Otherwise, we show a quick pick and allow the user to choose.

Then we invoke vscode.open which already handles ranges in the URI fragment for us.