[FLINK-7942] [table] Reduce aliasing in RexNodes

[twalthr]

What is the purpose of the change

This PR reduces the number of AS expressions in projects. This fixes the bug mentioned in FLINK-7942 with the FilterJoinRule and improves the plans. Many calc operations are not needed anymore. For multi-windows, the change caused some problems that are not trivial to fix, so they still use aliasing for resolving time attributes.

Brief change log

• Remove explicit alias expression from RexNodes

Verifying this change

• Added testFilterJoinRule in JoinTest.

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

[fhueske]

Thanks for the PR @twalthr!

This change seems to result in a plan regression for over window aggregates because projections are no longer pushed down.

Thanks, Fabian

[fhueske]

The new plan is less efficient, because a projection isn't pushed down anymore and a wider row needs to be materialized in the over window.

[twalthr]

Thanks @fhueske. I simplified the changes a bit more. Now we use explicit aliases only for windows and the alias operator.

[fhueske]

Looks good. +1 to merge