Revive Observatory launching as a hidden action

The buttons for opening Observatory were recently removed. For things that DevTools doesn't handle (like traversing through live object instances), the Observatory is still a useful tool for developers who know how to use it.

Currently to get the Observatory URL for an app launched via IntelliJ, you have to open DevTools and extract the Observatory URL from the DevTools URL. This is unwieldy because it's percent encoded, and you end up spawning a DevTools instance that you aren't going to use.

Hidden actions can be surfaced in IntelliJ using Ctrl-Shift-A search. This allows devs to be directed to DevTools for their general needs, but those who know about the Observatory can get to it. Other hidden actions (like opening the settings registry) are also exposed this way, and VS Code has a similar "hidden action search" with Ctrl-Shift-P.

cc @devoncarew