Casts of collections of function types

TL;DR Casting collections of function types crashes at runtime. I've been working on a fix for ~10 months across three PRs: First PR was approved and merged, but it didn't handle some use cases and was reverted. Second PR follows the approach approved in the first PR also fixing identified gaps. But it got stuck in code review. There is a disagreement about the scope of the fix. Review feedback on the two PRs gives contradictory guidance about synthesizing ClosureExpr. I've got no response fro...