colexec: clean up handling of abandoned components

[yuzefovich]

During the planning of vectorized flows, there are scenarios when certain operators are abandoned after they have been created (i.e. they become optimized out of the tree). Examples are columnarizers being removed from the flow (3c54450) or special queries like SELECT 1 FROM t HAVING true for which we plan fixedNumTuplesNoInputOp with no inputs. This works well for the main tree for the execution purposes, but it can break the assumptions of DrainMeta/Close method implementations that Init has been called.

In #61306 (comment) Alfonso suggested a nice idea to keep track of this state during the planning and disabling certain components when they are abandoned.

Jira issue: CRDB-2974

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