[FLINK-11788][table-planner-blink] Support Code Generation for RexNode

[wuchong]

What is the purpose of the change

This is the basic implementation to support code generation for RexNodes.

Brief change log

Flink/Blink's code generation is not clean and the generate.... methods is existed in various util class (e.g. CodeGenUtils, BinaryStringCallGen, CallGenerator, ScalarOperators ...). This pull request does some code cleanup to put the generations into a new structure.

All the generate.... methods are split and placed into only 2 util classes.

• GenerateUtils: generate code for general purpose, e.g. generateCallIfArgsNotNull, generateFieldAccess, generateLiteral. It can be used in various CodeGenerator.
• SqlOperatorGens: generate code for SQL scalar operators, e.g. arithmetic operator. It is mostly used in ExprCodeGenerator.

Some other classes are:

• CallGenerator interface: generate a call, usually used when the generation depends on some additional parameters.
• CodeGenUtils: a utility for codegen, e.g. newName, primitiveTypeTermForType, but not include generate... methods.
• ExprCodeGenerator: responsible for generating codes for a given calcite RexNode.
• CodeGeneratorContext: context for code generator, maintaining various reusable statements

Verifying this change

Add a ExpressionTestBase base class to check the code generation for expressions(RexNode).

We introduce 5 expression validation test class and 9 expression test class.

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): (no)
• 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? (no)
• If yes, how is the feature documented? (not applicable)

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[KurtYoung]

Could you add some comments to these newly introduced variables to explain what these are used for?

[wuchong]

Sure

[KurtYoung]

+1 to merge

[wuchong]

Rebased and squashed.

Waiting travis to turn green...