Avoid accessing global font settings from syntax highlighters

Change-Id: Ic015f7449351166ec41a7745355ddc63504f6442
Reviewed-by: André Hartmann <aha_1980@gmx.de>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/texteditor/syntaxhighlighter.h

@@ -69,6 +69,7 @@ public:
 
     // Don't call in constructors of derived classes
     virtual void setFontSettings(const TextEditor::FontSettings &fontSettings);
+    TextEditor::FontSettings fontSettings() const;
 
     void setNoAutomaticHighlighting(bool noAutomatic);