Support accessing members of a conditional value

[ranma42]

This changeset adds support for accessing a member of the result of a conditional expression.

It achieves this by folding the member access into the conditional.

Fixes #34589.

[ranma42]

Note that the updated baselines point to a missing CASE simplification (CASE WHEN nonNullableX THEN TRUE ELSE FALSE END -> nonNullableX).
Additionally, the test I implemented currently hits #28077 (neither join is really needed).

I would like to add a couple of missing test cases before marking as ready:

• different subclasses of a same type (see point 2 in Support projecting different navigations (but same type) via conditional operator #34589 (comment) )
• select'ing the conditional, then accessing multiple members

I am also thinking that it might be a good idea to write the tests so that they do not interact with #28077, so I will probably end up rewriting the existing test. What is the best place for these tests? (if I want to check the behavior on different subclasses, maybe InheritanceQueryTestBase makes more sense 🤔 )