perf(ui): gallery / image perf

[psychedelicious]

Summary

The gallery was getting very slow.

On main, on FF in dev mode, after loading 2 pages of the gallery so the images are cached, switching between them took ~105ms across 7 renders.

With the changes in this PR, that's down to ~55ms across 3 renders.

This translates to the initial load of gallery pages and switching tabs in the app. Feels way better.

Specific changes:

• Refactor image context menu to be a singleton. Previously, we were creating a new context menu component for every visible image. When changing pages in the gallery, we had to create new menu components, which was hugely wasteful. Now there is a single context menu and we just update the image it is for, as it is opened.
• Defer a lot of logic in IAIDndImage & GalleryImage (rendering components, calling hooks) until it's actually needed. We were spending a lot of time doing calculations or renders for things would likely never be used.
• Memoize a handful of components.

Tested on FF, Safari, Chrome and iOS Safari. Makes a really big difference on iOS.

Related Issues / Discussions

n/a

QA Instructions

Poke around the gallery. Should feel snappier.

Merge Plan

n/a

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• Documentation added / updated (if applicable)

[hipsterusername]

Oh this is smooooth.