This commit splits the flink-table module into multiple submodules in
accordance with FLIP-32 (step 1).

The new module structure looks as follows:

flink-table-common
       ^
       |
flink-table-api-java <------- flink-table-api-scala
       ^                                 ^
       |                                 |
flink-table-api-java-bridge    flink-table-api-scala-bridge
       ^
       |
flink-table-planner

The module structure assumes that the type system has been reworked such
that only one table environment exists for both Java and Scala users.

The module `flink-table-planner` contains the content of the old
`flink-table` module. From there we can distribute ported classes to
their final module without breaking backwards compatibility or
force users to update their dependencies again.

For example, if a user wants to implement a pure table program in Scala,
`flink-table-api-scala` and `flink-table-planner` need to be
added to the project.

Until we support pure table programs, `flink-table-api-scala/java-bridge`
and `flink-table-planner` need to be added to the project.

This closes #7587.