Add accessors for underling wxTextCtrl GTK widgets

Allow retrieving GtkTextBuffer or GtkEditable used for multi- and
single-line controls respectively.

Closes #23829.

include/wx/gtk/textctrl.h

@@ -11,6 +11,8 @@
 #define _WX_GTK_TEXTCTRL_H_
 
 typedef struct _GtkTextMark GtkTextMark;
+typedef struct _GTKGetTextBuffer GTKGetTextBuffer;
+typedef struct _GTKGetEditable GTKGetEditable;
 
 //-----------------------------------------------------------------------------
 // wxTextCtrl
@@ -186,6 +188,11 @@ protected:
     void GTKSetWrapMode();
     void GTKSetJustification();
 
+    // get the underlying text buffer for multi-line controls, or null otherwise
+    GtkTextBuffer *GTKGetTextBuffer() { return IsMultiLine() ? m_buffer : nullptr; }
+    // get the underlying text control
+    GtkEditable *GTKGetEditable() const { return GetEditable(); }
+
 private:
     void Init();
 

interface/wx/textctrl.h

@@ -1791,6 +1791,42 @@ public:
 
     ///@}
 
+    /**
+        @name Gtk-specific functions
+    */
+    ///@{
+
+    /**
+        Gets the underlying text buffer for multi-line controls.
+
+        This function returns the underlying GTK object for multiline text
+        controls, i.e. those with wxTE_MULTILINE style, and @NULL for single
+        line text controls.
+
+        Having direct access to the `GtkTextBuffer` allows to use GTK API
+        directly if necessary, but beware that doing it may interfere with the
+        normal wxTextCtrl operation.
+
+        @onlyfor{wxgtk}
+
+        @since 3.3
+    */
+    GtkTextBuffer *GTKGetTextBuffer();
+
+    /**
+        Gets the underlying text control that can be uses with GTK’s API.
+
+        This function can only be called for single-line text controls, i.e.
+        those without wxTE_MULTILINE style.
+
+        @onlyfor{wxgtk}
+
+        @since 3.3
+    */
+    GtkEditable *GTKGetEditable();
+
+    ///@}
+
     ///@{
     /**
         Operator definitions for appending to a text control.