Add site context menu

[ndiego]

Proposed Changes

This PR adds a context menu to sites in the sidebar, and was originally designed last year:

While a relatively low-priority feature, the context menu is a significant QOL improvement, especially for Studio power users. Simple actions like deleting a site now take three clicks rather than up to five clicks.

This PR does not add new functionality to Studio, such as the "Duplicate site..." option shown in the design mockup above. It simply adds easy access to all the existing functionality in Studio.

Here are the various states:

Stopped	Started	Starting up (isLoading)	Adding Site (isAddingSite)

A couple of notes:

• The "Open in..." options respect the user preferences
• "Edit site..." will switch to the Settings tab of the correct site and then open up the "Edit site" modal
• Theoretically, everything should work regardless of operating system, but I do not have a Windows machine to test

Here's a quick video of this feature in action:

studio-context-menu.mp4

Testing Instructions

• Add a new site if none exist
• Open the context menu and try all the options

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[sejas]

Great work Nick! 🎉
Thanks for adding the site context menu.
I've pushed a commit fixing the tests. I'll take a closer look next week, but feature wise, everything worked smoothly.

One suggestion, what do you think if we leave open site and open wp-admin enabled for stopped sites too?
We could start the site before opening the browser.

[ndiego]

One suggestion, what do you think if we leave open site and open wp-admin enabled for stopped sites too?
We could start the site before opening the browser.

@sejas, good call. I was just following the original design, but the other "Open site" and "WP admin" links in the app start up the site if it has not already been started.

I updated the functionality in d1fa0db