Clean up METADATA files

* The toplevel was missing a LICENSE compliant with
  go/compliancelint-checks#AllLicensesRecorded, which requires
  identifying all the child licenses used (and suggests identifying the
  source files covered).

* Updated the toplevel METADATA file to briefly describe the contents.
  Note that the Android METADATA files do not support
  `third_party { ... type: Group ... }` which better matches how this
  subproject is organized.

* The lint checks also required a `url { }` block in the `third_party {
  }` block. This adds one.

* Distinguish the chromium.org protocols from the freedesktop.org
  protocols.

* Some of the chromium.org protocols are under the
  "components/exo/wayland/protocol" path. Add that to the METADATA file.
  A future clean import will clean up the local file organization to
  match the upstream organization.

Bug: 337365602
Test: This CL has no lint warnings in Gerrit.
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:570d84609c88464cbe36fb3e0b5a4d4cf28f5ed4)
Merged-In: I07e0415b577247d5047460eb825c2a93cfa336a2
Change-Id: I07e0415b577247d5047460eb825c2a93cfa336a2
4 files changed