Clang: Provide tooltips

This includes also the query data for the help system (F1) for an
identifier under cursor.

Regressions (libclang changes necessary):
 - Function signatures do not contain default values.
 - Aliases are not resolved for/at:
   - template types
   - qualified name of a type

Fixes/Improvements:
 - Resolve "auto"
 - On a template type, show also the template parameter.
 - For a typedef like
     typedef long long superlong;
   the tooltip was "long long superlong", which was confusing.
   Now, "long long" is shown.

New:
 - Show first or \brief paragraph of a documentation comment.
 - Show size of a class at definition.
 - Show size of a field member in class definition.

Task-number: QTCREATORBUG-11259
Change-Id: Ie1a07930d0e882015d07dc43e35bb81a685cdeb8
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

tests/unit/unittest/mockclangcodemodelclient.h

@@ -45,4 +45,6 @@ public:
                  void(const ClangBackEnd::ReferencesMessage &message));
     MOCK_METHOD1(followSymbol,
                  void(const ClangBackEnd::FollowSymbolMessage &message));
+    MOCK_METHOD1(tooltip,
+                 void(const ClangBackEnd::ToolTipMessage &message));
 };