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

In #24296, 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.