WebUI: Migrate cr-url-list-item to CrLitElement

Also adding a Lit version of the relatively small MouseHoverableMixin,
which is used by this element.

Bug: 40943652
Change-Id: I5b83c66802961795f1cc1732d525a1c033d62a56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5406082


Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280333}