[FLINK-14903][table] Relax structured types constraints

[twalthr]

What is the purpose of the change

In order to allow type extraction of structured types that are not registered in a catalog, we need to relax the structured type concept to "inline or anonymous structured types" that are not identified by an object identifier in a catalog but the fully qualified implementation class.

This PR also fixes issues with UnresolvedIdentifier

Brief change log

• Use UnresolvedIdentifier everywhere
• Fix equals of UnresolvedIdentifier
• Make ObjectIdentifier optional for anonymous structured types

Verifying this change

This change is already covered by existing tests.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): yes
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? yes
• If yes, how is the feature documented? JavaDocs

[flinkbot]

Thanks a lot for your contribution to the Apache Flink project. I'm the @flinkbot. I help the community
to review your pull request. We will use this comment to track the progress of the review.

Automated Checks

Last check on commit be6f37a (Wed Dec 04 15:53:45 UTC 2019)

Warnings:

• No documentation files were touched! Remember to keep the Flink docs up to date!

_{Mention the bot in a comment to re-run the automated checks.}

Review Progress

• ❓ 1. The [description] looks good.
• ❓ 2. There is [consensus] that the contribution should go into to Flink.
• ❓ 3. Needs [attention] from.
• ❓ 4. The change fits into the overall [architecture].
• ❓ 5. Overall code [quality] is good.

Please see the Pull Request Review Guide for a full explanation of the review process.

Details

The Bot is tracking the review progress through labels. Labels are applied according to the order of the review items. For consensus, approval by a Flink committer of PMC member is required

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot approve description to approve one or more aspects (aspects: description, consensus, architecture and quality)
• @flinkbot approve all to approve all aspects
• @flinkbot approve-until architecture to approve everything until architecture
• @flinkbot attention @username1 [@username2 ..] to require somebody's attention
• @flinkbot disapprove architecture to remove an approval you gave earlier

[flinkbot]

CI report:

• 73831c7 : SUCCESS Build
• be6f37a : SUCCESS Build

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run travis re-run the last Travis build

[dawidwys]

I had some smaller nitpicking comments.

[dawidwys]

I think this logic is duplicated in UnresolvedIdentifier.of. We could create the UnresolvedIdentifier as UnresolvedIdentifier.of(parts.toArray())

[dawidwys]

nit: Personally I would not use is prefix for setters. I'd use this prefix only for getters. How about just nullable?

[dawidwys]

nit: This is really nitpicking. How about extracting the instantiation of new builder and duplicating the attributes to separate methods. The visit method is already quite long.

[twalthr]

Thanks for the feedback @dawidwys. Merging...