Linear types: make 'undefined x' linear in 'x' (#18731)
This fixes #18731 (closed).
In matchActualFunTySigma
, when faced with a function we always used the Many multiplicity. This made undefined x
unrestricted in x
, even though it could be linear.
The number in dynamic-paper
test gets slightly larger, but there are no large changes in the perf testsuite, so I'm not counting this as a problem.