Clang: Extract highlighting information

Prepare the move of the semantic highlighting to the clang back end. We
have it under tests too so it should be quite easy to make changes or
corrections.

Change-Id: I5706a8a06fde5a9ba2eba3a8ba62782102ac0bd3
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>

src/libs/sqlite/utf8string.h

@@ -86,6 +86,7 @@ public:
     bool startsWith(const char *text) const;
     bool startsWith(char character) const;
     bool endsWith(const Utf8String &text) const;
+    bool isNull() const;
     bool isEmpty() const;
     bool hasContent() const;