It is required to traverse the chain of "and" boolean expressions.

At the moment we don't add tests as upcoming equality propagation
would implement enough tests for this scenario.

We don't want to mess with subqueries in projection as our query
set doesn't contain such queries. It also simplifies some
transformations (equality propagation for example).

This low-level function can be helpfull to construct rows with a
mix of references and constants.

Previously, row expressions (i.e. tuples) expected to have alias
nodes in the list. It is correct for relational node output, but
for selection filters and join conditions we don't need aliases.
So, add api to produce rows with and without aliases.

Previously, we didn't pass logaicl ID, that was incorrect we have
to generate ID first for the filter boolean expression, and then
pass it to the selection node as well.

Add a test for successfull Plan::add_union_all() run.

Also fix some documetation style

Also make a "add_bool" test fixup

We need this refactoring to move all node plan methodes to the new
Nodes structure. Otherwise we have to put a mutable lock for the
whole plan structure rather then on the nodes list. It makes
porblems with API refactoring otherwise.

Also move this Plan implementation method to expressions.