[AutoDiff] Fix PullbackCloner tangent value category mismatch issues.

Fix SIL pullback function type calculation: remap original `unowned` results to
the correct pullback parameter convention depending on the `TangentVector` type
lowering.

Make `PullbackCloner` visitors for the following instructions check and handle
tangent value categories: `struct`, `struct_extract`, `tuple`, `destructure_tuple`.

Add differentiation tests for `Optional` struct and class stored properties,
exercising the instruction visitors above.

Resolves SR-13430.

Author: dan-zheng

lib/SIL/IR/SILFunctionType.cpp

@@ -538,6 +538,8 @@ static CanSILFunctionType getAutoDiffPullbackType(
         TC.getTypeLowering(pattern, tanType, TypeExpansionContext::minimal());
     ParameterConvention conv;
     switch (origResConv) {
+    case ResultConvention::Unowned:
+    case ResultConvention::UnownedInnerPointer:
     case ResultConvention::Owned:
     case ResultConvention::Autoreleased:
       if (tl.isAddressOnly()) {
@@ -547,10 +549,6 @@ static CanSILFunctionType getAutoDiffPullbackType(
                               : ParameterConvention::Direct_Guaranteed;
       }
       break;
-    case ResultConvention::Unowned:
-    case ResultConvention::UnownedInnerPointer:
-      conv = ParameterConvention::Direct_Unowned;
-      break;
     case ResultConvention::Indirect:
       conv = ParameterConvention::Indirect_In_Guaranteed;
       break;