Clang: Use current TranslationUnit follow symbol based on clang code model

It might be quite a safe replacement which can fix builtin
code model issues.

If clang code model fails to follow symbol or does not find
a definition when it's required we fall back to the built-in
code model to proceed with project-wide follow symbol.

To make it almost a full replacement tweak include paths underline
on cursor hover to match what we have in built-in code model.

SIGNAL/SLOTS macros are not yet supported but can be handled
in follow up patch.

Task-number: QTCREATORBUG-19477
Change-Id: Id1611511d661a8aaf3e93502b4e03e1792c7c1d3
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

tests/unit/unittest/clangcodemodelserver-test.cpp

@@ -92,6 +92,17 @@ MATCHER_P5(HasDirtyDocument,
     }
 }
 
+MATCHER_P(PartlyContains, token, "")
+{
+    for (const auto &item: arg) {
+        if (item.types == token.types && item.line == token.line && item.column == token.column
+                && item.length == token.length) {
+            return true;
+        }
+    }
+    return false;
+}
+
 static constexpr int AnnotationJobsMultiplier = 2;
 
 class ClangCodeModelServer : public ::testing::Test
@@ -675,7 +686,7 @@ void ClangCodeModelServer::expectDocumentAnnotationsChangedForFileBWithSpecificH
     EXPECT_CALL(mockClangCodeModelClient,
                 documentAnnotationsChanged(
                     Field(&DocumentAnnotationsChangedMessage::tokenInfos,
-                          Contains(tokenInfo))));
+                          PartlyContains(tokenInfo)))).Times(AnnotationJobsMultiplier);
 }
 
 void ClangCodeModelServer::updateUnsavedContent(const Utf8String &filePath,