[FLINK-12690][table-api] Introduce a Planner interface

[dawidwys]

What is the purpose of the change

This PR introduces the Planner interface that should serve as a bridge between API and planner modules.

Brief change log

• 9a8ae5a - this commit moves the StreamTransformation from flink-streaming to flink-core. This is necessary so that we do not add dependency on flink-streaming to flink-table-api
• Added Planner interface that defines methods to parse sql statements and convert relational TableOperation program to StreamTransformations
• Introduced ModiyTableOperations which definy a way to exit the Table ecosystem. This way we can provide either TableSink to emit to or the expected type information of the produced StreamTransformations

Verifying this change

This change introduces only new interface that are not used yet, therefore no tests are added.

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)