Move UriCodec to be near its one user

The only user of UriCodec is android.net.Uri so it can
be moved to android.net.

This change moves the UriCodecTest to the unit tests
and there is an associated change to Uri's CTS tests
to ensure we're testing public method behavior there too.

Test: make droid && make cts
Bug: 111055375
Change-Id: Id032f849b439adf3fd7cb1a3c8b234a5eec68fac