ESQL: Refactor Join inside the planner (#115813)

[costin]

First PR that introduces a Join as a first class citizen in the planner.
Previously the Join was modeled as a unary node, embedding the right
side as a local relationship inside the node but not exposed as a child.
This caused a lot the associated methods (like references, output and
inputSet) to misbehave and the physical plan rules to pick incorrect
information, such as trying to extract the local relationship fields
from the underlying source - the fix was to the local relationship
fields as ReferenceAttribute (which of course had its own set of
issues). Essentially Join was acting both as a source and as a streaming
operator.

This PR looks to partially address this by:

• refactoring Join into a proper binary node with left and right
  branches which are used for its references and input/outputSet.
• refactoring InlineStats to prefer composition and move the Aggregate
  on the join right branch. This reuses the Aggregate resolution out of
  the box; in the process remove the Stats interface.
• update some of the planner rules that only worked with Unary nodes.
• refactor Mapper into (coordinator) Mapper and LocalMapper.
• remove Phased interface by moving its functionality inside the planner
  (no need to unpack the phased classes, the join already indicates the
  two branches needed).
• massage the Phased execution inside EsqlSession
• improve FieldExtractor to handle binary nodes
• fix incorrect references in Lookup
• generalize ProjectAwayColumns rule

Relates #112266

Not all inline and lookup tests are passing:

• 2 lookup fields are failing due to name clashes (qualifiers should
  fix this)
• 7 or so inline failures with a similar issue

I've disabled the tests for now to have them around once we complete
adding the functionality.

(cherry picked from commit 4ee98e8)
(cherry picked from commit 681f509)