We allow ListWidget instances to pass functions in opts that can
be called after scrolling to determine when to render.
Also, allow a callback function to be called pre render.
This improves the UX of creating a stream for atleast 1000+ users
realm by showing the the stream creation form much faster than
before.
Search, user addition, scrolling worked smoothly on 15k+
users realm as tested on dev setup.
Also, simplebar is used to replace the default scrollbar.
Fixes#16805
Now when we want to measure how long a block
of code takes to execute, we just wrap it with
`blueslip.measure_time`, instead of the awkward
idiom from my original commit of getting a callback
function.
My rationale for the original scheme was that I
wanted to minimize diffs and avoid changing
`const` to `let` in a few cases, but I believe
now that the function wrapper is nicer.
In a few cases I just removed the blueslip timing
code, since I was able to confirm on czo that
the times were pretty minimal.
Aman Agrawal
Anders Kaseorg
Steve Howell
Rohitt Vashishtha