[WebParagraph] Initial wiring for the experimental WebParagraph implementation (#167763)

In this PR:
- `felt build --experimental-webparagraph` builds a 3rd variant of
CanvasKit to be used for `WebParagraph`.
- `felt test --suite=chrome-dart2js-experimental-webparagraph-ui` runs
`test/ui/` tests against `WebParagraph`.
- `felt test --suite=chrome-dart2js-experimental-webparagraph-ui` runs
Chrome with the extra flag:
    - `--enable-experimental-web-platform-features`

In the future:
- Upgrade to Chrome@133.0.6943.53 or above.
- Actual implementation and tests of WebParagraph coming in
https://github.com/flutter/flutter/pull/167559
- Run the `chrome-dart2js-experimental-webparagraph-ui` suite in CI.
- Trim the new experimental build of CK to realize the reduction in
size.