Dispatch timing events when inserting/removing SMIL elements

When a SMIL animation element is inserted into a document where the SMIL
timeline is running, and the animation elements' timing interval is
active, no 'beginEvent' event would be dispatched, because
UpdateActiveState() would not notice the state transition. Similarly for
the 'endEvent', which would not "end" if it was removed from the
document when it was active.

Explicitly dispatch the relevant events when an animation element is
added or removed from the time container and the time container has
started.

This addresses the timeouts in the href-animate-element.html and
href-mpath-element.html tests, but failures remain due to other issues
(not updating the animation value synchronously).

Bug: 40118791
Change-Id: I52565562e7338b119ee5b31421ab7dc62ca254e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5412942
Auto-Submit: Fredrik Söderquist <fs@opera.com>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1282206}