Fix isTriviallyDuplicatable to handle open_pack_element

SILInstruction::clone doesn't know how to clone instructions that produce
the archetype uuid. SILCloner is equipped to handle such instructions.

Optimizations like LoopRotate use  SILInstruction::clone and will be
incorrect for such instructions.

rdar://130047619

Author: meg-gupta

lib/SIL/IR/SILInstruction.cpp

@@ -1419,7 +1419,7 @@ bool SILInstruction::isTriviallyDuplicatable() const {
   if (isa<OpenExistentialAddrInst>(this) || isa<OpenExistentialRefInst>(this) ||
       isa<OpenExistentialMetatypeInst>(this) ||
       isa<OpenExistentialValueInst>(this) || isa<OpenExistentialBoxInst>(this) ||
-      isa<OpenExistentialBoxValueInst>(this)) {
+      isa<OpenExistentialBoxValueInst>(this) || isa<OpenPackElementInst>(this)) {
     // Don't know how to duplicate these properly yet. Inst.clone() per
     // instruction does not work. Because the follow-up instructions need to
     // reuse the same archetype uuid which would only work if we used a