Fuzzer: Emit try-delegate instructions

[tlively]

Add try-delegate generation to TranslateToFuzzReader::makeTry and update
fixAfterChanges to preserve DELEGATE_CALLER_TARGET on try-delegates.

Also fix three bugs uncovered by fuzzing delegate and add regression tests:

• Preserve concrete stack types on StackInst::Delegate in StackIRGenerator.
• Increment controlFlowDepth after printing the condition in
  PrintSExpression::visitIf and pop catchIndexStack on StackInst::Delegate in
  printStackIR.
• Use dynCast() instead of cast() when walking tryStack in
  CFGWalker.