Clang: Optimize clang overview model

Build the tree in only one loop.

clangbackend generates tokens almost as fast as it
did before (about 10% slower in general).
Broken documents are more affected and take much more
time (about 300%) but it's better to have this time spent
on backend side then in QtC itself.

Task-number: QTCREATORBUG-20205
Change-Id: I34c58bca30c4494005a029abd82c7e612ecd6fb9
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/clangcodemodel/clangeditordocumentprocessor.cpp

@@ -250,7 +250,6 @@ void ClangEditorDocumentProcessor::updateHighlighting(
         const auto skippedPreprocessorBlocks = toTextEditorBlocks(textDocument(), skippedPreprocessorRanges);
         emit ifdefedOutBlocksUpdated(documentRevision, skippedPreprocessorBlocks);
 
-        m_tokenInfos = tokenInfos;
         m_semanticHighlighter.setHighlightingRunner(
             [tokenInfos]() {
                 auto *reporter = new HighlightingResultReporter(tokenInfos);