Follows #212 and #2087

Note: this feature is already offered natively by pressing the i key. This issue discusses what else can be done, if anything.

Possible additions

• Add a tooltip on the menuitem explaining that they can press i to "toggle all"

• Trigger GitHub's own feature by simulating a keypress when the menu item is alt-clicked:

   document.dispatchEvent(new KeyboardEvent('keydown', {code: 'KeyI', key: 'i'}))

Alt-click

The alt-click solution was discussed at length in #2087 and its last iteration was this. It didn't work in Firefox.

1. Go to https://github.com/sindresorhus/refined-github/pull/1896/files#diff-745c47517b47e007eb2f34f4d2072fa0
2. Open the file's dropdown
3. Alt-click "✓ Show comments"

It should hide all the comment threads on the page, as part of toggle-everything-with-alt

Semi-related issue

#2329