Add GetCapabilities() to on device model service

This API allows querying what capabilities a model can support. This
will be used to determine if the model can be used for certain features.
This also updates chrome://on-device-internals to use this API to
automatically detect capabilities when starting the session.

Bug: 399200301
Change-Id: I5288bdd4b879f5d3a773d165f212940e7da3ece0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6353258
Reviewed-by: Austin Sullivan <asully@chromium.org>
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1432311}