Resolve "Text from the diff is showing within a table header inside the discussion after the discussion is resolved"

fixed up duplicate is-collapsed classes

this saves a load of computational stuff happening in the template
the data the template recieves is the data that should be rendered

When a request contains an ETag value in its If-None-Match header, the backend
may send a request ID (from Rack) that does not correspond to a value in Peek's
Redis cache (because we aborted the Rails processing in our ETag middleware).

Because a cached response (304) has to replace the headers with those from the
previous 200 - https://tools.ietf.org/html/rfc7234#section-4.3.4 - we add a
custom header that will only be present in cache hits, that can tell the
frontend to ignore these.

Closes #45412

Improves the web IDE commit message imput by highlighting any characters
on the first line after 50 & every other line after 72

Closes #44832

[ci skip] Adds specs

Adds specs

Move html to haml file instead of JS

Closes #45326