Clang: Show help with F1 even if there is a diagnostic

...at that particular location.

For example, the code

     new QSignalMapper;

produced a deprecated warning with Qt 5.12 and F1 led to "No
documentation available" as the diagnostic was always prioritized.

Task-number: QTCREATORBUG-21686
Change-Id: Icf03000fb6b9de04e467e758da6167018d154a21
Reviewed-by: Marco Bubke <marco.bubke@qt.io>
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/texteditor/basehoverhandler.h

@@ -71,6 +71,8 @@ protected:
     void setLastHelpItemIdentified(const HelpItem &help);
     const HelpItem &lastHelpItemIdentified() const;
 
+    bool isContextHelpRequest() const;
+
     void propagateHelpId(TextEditorWidget *widget, const Core::IContext::HelpIdCallback &callback);
 
     // identifyMatch() is required to report a priority by using the "report" callback.
@@ -87,6 +89,7 @@ private:
     QString m_toolTip;
     HelpItem m_lastHelpItemIdentified;
     int m_priority = -1;
+    bool m_isContextHelpRequest = false;
 };
 
 } // namespace TextEditor