Change wxRichTextParagraph::m_cachedLines data type to vector

Now wxRichTextParagraph::m_cachedLines is stored as a wxVector instead
of a wxList.

See #2523, closes #2577.

interface/wx/richtext/richtextbuffer.h

@@ -4305,7 +4305,7 @@ protected:
 #endif
 };
 
-class wxRichTextLineList;
+typedef wxVector<wxRichTextLine*> wxRichTextLineVector;
 
 /**
     @class wxRichTextParagraph
@@ -4357,7 +4357,7 @@ public:
     /**
         Returns the cached lines.
     */
-    wxRichTextLineList& GetLines() { return m_cachedLines; }
+    const wxRichTextLineVector& GetLines() const { return m_cachedLines; }
 
 // Operations
 
@@ -4482,7 +4482,7 @@ public:
 protected:
 
     // The lines that make up the wrapped paragraph
-    wxRichTextLineList  m_cachedLines;
+    wxRichTextLineVector m_cachedLines;
 
     // Whether the paragraph is impacted by floating objects from above
     int                 m_impactedByFloatingObjects;