[FLINK-11865] Improve code generation speed in TraversableSerializer

[igalshilman]

What is the purpose of the change

The TraversableSerializer is generating, at runtime, code that evaluates to an instance of a CanBuildFrom. This operation makes job submissions/translation prohibitively slow, and must be cached.
This PR adds a cache to the TraversableSerializer.

Brief change log

• da624a4 Minor refactoring
• 03f18df Add and use the cache

Verifying this change

This change is already covered by existing tests, such as TraversableSerializerSnapshotMigrationTest

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

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

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

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• ❓ 1. The [description] looks good.
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  • Needs attention by @aljoscha [PMC]
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[igalshilman]

@flinkbot attention @aljoscha

[aljoscha]

Merged