[RemoteAST] Fix metadata reader to properly read tuple type metadata

Because `readMetadata` correctly reads tuple type metadata bounds,
there is no need to call for remote read of the memory allocated
for element types, since they are going to be laid out right after
tuple metadata itself and could be accessed using accessors in
`TargetTupleTypeMetadata`.

Author: xedin

include/swift/Remote/MetadataReader.h

@@ -777,16 +777,8 @@ class MetadataReader {
       std::vector<BuiltType> elementTypes;
       elementTypes.reserve(tupleMeta->NumElements);
 
-      StoredPointer elementAddress = MetadataAddress +
-        sizeof(TargetTupleTypeMetadata<Runtime>);
-      using Element = typename TargetTupleTypeMetadata<Runtime>::Element;
-      for (StoredPointer i = 0; i < tupleMeta->NumElements; ++i,
-           elementAddress += sizeof(Element)) {
-        Element element;
-        if (!Reader->readBytes(RemoteAddress(elementAddress),
-                               (uint8_t*)&element, sizeof(Element)))
-          return BuiltType();
-
+      for (unsigned i = 0, n = tupleMeta->NumElements; i != n; ++i) {
+        auto &element = tupleMeta->getElement(i);
         if (auto elementType = readTypeFromMetadata(element.Type))
           elementTypes.push_back(elementType);
         else
@@ -1226,8 +1218,8 @@ class MetadataReader {
         if (!Reader->readInteger(RemoteAddress(numElementsAddress),
                                  &numElements))
           return nullptr;
-        auto totalSize = sizeof(TargetTupleTypeMetadata<Runtime>)
-          + numElements * sizeof(StoredPointer);
+        auto totalSize = sizeof(TargetTupleTypeMetadata<Runtime>) +
+                         numElements * sizeof(TupleTypeMetadata::Element);
 
         // Make sure the number of elements is reasonable
         if (numElements >= 256)