WebUI: Fix cases that relied on bubbling '-changed' CrLitElement events.

'-changed' notification events fired from CrLitElement when a reactive
property is configured with "notify: true" shouldn't be bubbling across
ShadowDOM boundaries, to match their Polymer counterparts which they are
emulating. Fixing cases that relied on this as a preparatory step to
changing such events to not bubble.

Some cases required updating prod code to propagate '-changed' events
across ShadowDOM boundaries, by adding "notify: true" and '-changed'
listeners in intermediate DOM layers. Other cases, only required
updating tests, mostly in cases where a settings-radio-group was
involved, and changing to use the 'change' instead of
'selected-changed'. In other cases, waiting for microtasksFinished() was
necessary, since none of the events above were fired.

Bug: 402806151
Change-Id: Ie2a016680571b72a7b476ab68e63c49ee452d42c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6355164
Auto-Submit: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1433065}