[FLINK-34476][table-planner] Consider assignment operator during TVF column expansion

[twalthr]

What is the purpose of the change

Considers the assignment operator => when performing metadata virtual column expansion.

Enabling e.g. the following query:

TUMBLE(DATA => TABLE t3, TIMECOL => DESCRIPTOR(t3_m_virtual), SIZE => INTERVAL '1' MINUTE))

Brief change log

• Additional checks for SqlKind.ARGUMENT_ASSIGNMENT in the SQL validator.

Verifying this change

This change added tests and can be verified as follows:

ColumnExpansionTest#testExplicitTableWithinTableFunctionWithNamedArgs

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, Kubernetes/Yarn, 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

[flinkbot]

CI report:

• f96077b Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[dawidwys]

lgtm