WebUI: Make cr-lottie Worker TrustedTypes compliant, attempt 2.

The previous attempt at crrev.com/c/4039783/ only partially achieved its
stated goal. It modified the creation of cr-lottie's web worker to be
TrustedTypes compliant, but the worker itself was throwing a TT related
error asynchronously, which was unfortunately missed by tests.

During the attempt to enable TrustedTypes CSP checks on
chrome://webui-test/ where cr-lottie's unit tests are running from, it
was discovered that the worker was not actually working as expected, on
contexts with TT checks enabled (like chrome://settings).

Fixing by migrating away from importScripts(), and loading cr-lottie's
worker wrapper script as an ES module, which in turn allows it to import
the actual worker script using the following import statement

import 'chrome://resources/lottie/lottie_worker.min.js';

which does not trigger the TT related error thrown by importsScripts().
In order for this to work, also had to add chrome://resources in the
'worker-src' CSP of every WebUI page that uses cr-lottie.

Bug: 1098690,1385477
Fixed: 1399335
Change-Id: I204f7efd741ca5f2f7aeb4385dfa21dc20c59a82
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4086647
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1080990}