[clang][transformer] Change name range-selector to return Error instead of an invalid range.

Previously, when the text in selected range was different from the decl's name, `name` returned an invalid range, which could cause crashes if `name` was nested in other range selectors that  assumed always valid ranges. With this change, `name` returns an `Error` if it can't get the range.

Author: yuhaouy

clang/lib/Tooling/Transformer/RangeSelector.cpp

@@ -205,8 +205,12 @@ RangeSelector transformer::name(std::string ID) {
       // `foo<int>` for which this range will be too short.  Doing so will
       // require subcasing `NamedDecl`, because it doesn't provide virtual
       // access to the \c DeclarationNameInfo.
-      if (tooling::getText(R, *Result.Context) != D->getName())
-        return CharSourceRange();
+      StringRef Text = tooling::getText(R, *Result.Context);
+      if (Text != D->getName())
+        return llvm::make_error<StringError>(
+            llvm::errc::not_supported,
+            "Failed to get the name range for the decl. Name is " +
+                D->getName() + ", but range is " + Text);
       return R;
     }
     if (const auto *E = Node.get<DeclRefExpr>()) {