[ts] Type-check ui/FilterBar.js with TypeScript
[ts] Type-check ui/FilterBar.js with TypeScript

This CL includes two refactorings:
  * Replacing a custom property on HTMLElement with a WeakMap
  * Replacing an object thats used as a Map<string, boolean> with a Set

R=dba8716ee7f8d16236046f74d2167cb94410f6ed@chromium.org

Bug: chromium:1011811
Change-Id: Ie2185cdcb240bb9afacb6a75da377638c7e75be2
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2367936
Commit-Queue: Simon Zünd <38944668e9e2ca98ccd0275b53370f90fa55c113@chromium.org>
Reviewed-by: Tim van der Lippe <dba8716ee7f8d16236046f74d2167cb94410f6ed@chromium.org>

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