Arity: Require called *exactly once* for eta exp with -fpedantic-bottoms (#24296)

In #24296 (closed), we had a program in which we eta expanded away an error despite the presence of -fpedantic-bottoms. This was caused by turning called at least once lambdas into one-shot lambdas, while with -fpedantic-bottoms it is only sound to eta expand over lambdas that are called exactly once. An example can be found in Note [Combining arity type with demand info].

Fixes #24296 (closed).