Switch closure-loading instructions to be operands #2447
Description
We would like to switch LoadImplicitClosure and LoadFrameClosure to be simple operands, to reduce the complexity of code surrounding them. Unfortunately, in order to make LoadImplicitClosure into an operand (PassedBlock), Operand#retrieve needs to receive the passed block. That cascades into changes to Instr#interpret and callers of each. At the moment it was deemed "polishing the diamond", too big and too risky for too little gain. I will provide a patch based on the almost-complete version (minus the massive refactoring).