[FLEDGE] Add some initial WPT tests.

The first set of tests cover join/leave return values and argument
verification, auctions failing due to errors, sendReportTo(), and
some reportResult()/reportWin() argument validation tests.

There are still a huge number of untested FLEDGE features, this is
just intended as a starting point.

Bug: 1425952
Change-Id: I17d6da24eaf826b4771ea39466ab0b3bd57816a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4327953
Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: Dominic Farolino <dom@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1120173}