[FLINK-18090] Update the Row.toString method

[twalthr]

What is the purpose of the change

This updates the Row.toString method to provide a good summary string.

In particular it fixes the following issues:

• Changeflag: According to FLIP-95, a row describes an entry in a changelog. Therefore, it should visible whether a row is an insert, delete, or update change. Now indicated with +I, -D, +U, -U.
• Nested rows: In the old implementation it was not visible whether nested rows exist or not due to missing start/end boundaries. Now indicated with [...] or {...}.
• Positioned rows vs. named rows: According to FLIP-136, it should be visible whether a row operates in name-based or position-based field mode. Now indicated with [...] or {...}.
• Nested arrays in maps and lists: In the old implementation arrays in maps or lists could not be represented.
• Wrong formatting: Most programming languages use a space after a comma.

Brief change log

Because this change might cause issues for tests, we provide a flag in RowUtils for legacy mode and a JUnit rule to make the migration incremental.

All tests in modules apart from the Blink planner/runtime module have been updated.

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): yes
• 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, Kubernetes/Yarn/Mesos, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

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Automated Checks

Last check on commit 7b8a1e7 (Fri May 28 07:02:10 UTC 2021)

Warnings:

• 1 pom.xml files were touched: Check for build and licensing issues.
• No documentation files were touched! Remember to keep the Flink docs up to date!

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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.

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CI report:

• 7ca6a4f Azure: SUCCESS
• 7b8a1e7 Azure: PENDING

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[dawidwys]

+1 % Azure

[dawidwys]

Add a note it should be used only in tests?