[sil] Change SILType::getOptionalType() to use CanType::wrapInOptionalType() instead of rolling its own.

Author: gottesmm

lib/SIL/IR/SILType.cpp

@@ -88,10 +88,8 @@ SILType SILType::getBuiltinWordType(const ASTContext &C) {
 }
 
 SILType SILType::getOptionalType(SILType type) {
-  auto &ctx = type.getASTContext();
-  auto optType = BoundGenericEnumType::get(ctx.getOptionalDecl(), Type(),
-                                           { type.getASTType() });
-  return getPrimitiveType(CanType(optType), type.getCategory())
+  return getPrimitiveType(type.getASTType().wrapInOptionalType(),
+                          type.getCategory())
       .copyingMoveOnlyWrapper(type);
 }