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What does this MR do and why?

Load comments faster

Suggested improvements:

• Load notes before/after in correct position. Currently it just puts the note at the top of the list and adds things below it. Or we could pin it like !137544 (merged)
• Handle discussion replies (they load but not shown as nested, so they jump across while loading)

Screenshots or screen recordings

Comment is visible 12s earlier. Total loading time is the same.

Before	After
before	after

How to set up and validate locally

1. In rails console enable the experiment fully

   Feature.enable(:instant_notes)

2. Go to an issue with a lot of notes, then link to a note directly