personalization: add polymer and mojom API

Continue setting up personalization SWA. Add mojom API stub
to to check mojom is wired correctly. Implement mojom API
in a //chrome delegate because it will require access
to //chrome code when fully implemented.
Set up polymer build and add first polymer element.

BUG=b:181378252

Cq-Include-Trybots: luci.chrome.try:linux-chromeos-chrome
Change-Id: Ice470c54404ff7781ffe910828aeefbe8ba005a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2738376


Commit-Queue: Jeffrey Young <cowmoo@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Reviewed-by: Jimmy Gong <jimmyxgong@chromium.org>
Cr-Commit-Position: refs/heads/master@{#866185}