Fix live metrics memory leak

There are two main issues at play here:

1) web-vitals-inject.ts uses global arrays to monkeypatch Event
Listeners and Performance Observers (and their args!) and never removes
these when the Event Listeners and POs are finished with. I believe this
is the main memory leak. Gemini suggested a better alternative.

2) The web-vital.js library tracks the event entries into pendingGroups
for two reasons: i) to allow them to be emitted in the object should the
user wish to use them for some reason, and ii) to handle out of order
LoAFs. DevTools doesn't use them and also emits the entries right away
so does not benefit from holding on to them. This only is a problem for
really slow frames (as the demo in b/484342204 highlights) and we should
only keep the top 50 + 10, but that can still really add up and, as I
say, it is not actually needed for DevTools usage of web-vitals.js
anyway.

I'm going to do more clean up in web-vitals 5.2 (reducing the 50 to 5
and capping the queued entries to 5 as well, and Jack has a onIdleOrHidden fix as well), but for now this seems to solve the main issue in DevTools. We can have the Chat team test in Canary, once this lands.

Bug: 484342204
Change-Id: I7c4575289a4df76e8e29bee112aabc32831ad5d1
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/7644771
Reviewed-by: Jack Franklin <jacktfranklin@chromium.org>
Commit-Queue: Barry Pollard <barrypollard@chromium.org>
Reviewed-by: Paul Irish <paulirish@chromium.org>