MBS-13620: Convert the release editor's edit note tab to React

[mwiencek]

MBS-13620

Rather than a repeat of the relationship editor rewrite or EAA, I'm going to attempt to convert the release editor to React piecemeal, which should make it easier to test and review.

To start with, I've converted the edit note tab in this commit. This is a limited conversion: while it's now rendered with React, the component state is still managed by Knockout. Updates are propagated by calling render inside a computed observable, which works fine.

Eventually we'll want to manage all release editor state with a React reducer and remove all uses of Knockout, but I'll likely proceed with the rest of the conversion in the same way I've done here to start with.

Testing

I've tested both adding and editing releases. The two error messages and loading spinner worked for me; the edit previews, edit note, and "make votable" submission all worked fine too.