[User Education] Decouple HelpBubble mixin from HTML ids

This abstraction enables alternative methods of anchoring

Help bubbles are now identified by the element identifier instead of the anchor they attach to. By using native ids exclusively, the logic for listening for help bubble events and looking up help bubbles becomes much simpler. It also abstracts the dom from the mixin so we can use alternative methods of anchoring.

Tests were updated with minimal changes to get passing. I'll try to circle back and rework these, especially browser_tests.

Bug: 1378993
Change-Id: I530257b31813f429fb5176044cb80c326f948ea5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3986865
Reviewed-by: Dana Fried <dfried@chromium.org>
Commit-Queue: Mickey Burks <mickeyburks@chromium.org>
Auto-Submit: Mickey Burks <mickeyburks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1071866}