[clangd] Also use UTF-16 in index position.

[sammccall]

Oops, I missed this, thanks!
Possible to add a testcase? Any character that's not ASCII and is legal in an identifier should do it.
http://en.cppreference.com/w/cpp/language/identifiers

[sammccall]

(oops, meant to accept this - please do add a test if you can)

[hokein]

Add a test.

clangd/index/SymbolCollector.cpp

llvm::Optional<SymbolLocation> getSymbolLocation(
   if (!U)
     return llvm::None;
   FileURIStorage = std::move(*U);
   SymbolLocation Result;
   Result.FileURI = FileURIStorage;
   auto TokenLength = clang::Lexer::MeasureTokenLength(NameLoc, SM, LangOpts);
 
   auto CreatePosition = [&SM](SourceLocation Loc) {
-    auto FileIdAndOffset = SM.getDecomposedLoc(Loc);
-    auto FileId = FileIdAndOffset.first;
-    auto Offset = FileIdAndOffset.second;
+    auto LSPLoc = sourceLocToPosition(SM, Loc);
     SymbolLocation::Position Pos;
-    // Position is 0-based while SourceManager is 1-based.
-    Pos.Line = SM.getLineNumber(FileId, Offset) - 1;
-    // FIXME: Use UTF-16 code units, not UTF-8 bytes.
-    Pos.Column = SM.getColumnNumber(FileId, Offset) - 1;
+    Pos.Line = LSPLoc.line;
+    Pos.Column = LSPLoc.character;
     return Pos;
   };
 
   Result.Start = CreatePosition(NameLoc);
   auto EndLoc = NameLoc.getLocWithOffset(TokenLength);
   Result.End = CreatePosition(EndLoc);
 
   return std::move(Result);