Upgrade justinrainbow/json-schema to ~3.0

Upgrade justinrainbow/json-schema to ~3.0

The release between 1.6.1 and 3.0.0 has a huge amount of code
maintenance changes, as well as internal optimization and some
"visible" changes (as well as the one mentioned in the linked
task).

However, it's a version jump over 2 major versions, which is,
by it's definition a major change ;). Nonetheless, the (for us)
important api has changed marginally: Instead of using the
JsonSchema\Uri\UriRetriever class to retrieve the schema, we now use
the $ref keyword to reference the json schema file (which also is
an internal optimization). In this way, we let the json-schema library
decide, how to resolve a ref (and the schema) instead of relying
on the UriRetriever api to be public and stable.

The versions also include various bug fixes (which, as far as I know,
doesn't apply to us).

I tested this change with various combinations of valid and invalid
extension.json schemas (version 2 as well as version 3). Given that
there were no major changes to the schema interpretation itself, and
the good test coverage of the library, there shouldn't be a high risk
because of this change.

The full list of changes can be found at:
https://github.com/justinrainbow/json-schema/compare/1.6.1...3.0.0

as well as the changelogs of the single versions:
https://github.com/justinrainbow/json-schema/releases

Bug: T141281
Depends-On: I5687286da9f7fa2bb2b84699fa43ab3c2547fe03
Change-Id: Ie37e2ebc48684783abf8d99d2f775ee6a5988da7