Make wxDataViewCheckIconTextRenderer class public

Export this class, which was only used internally by wxTreeListCtrl
before, so that user code can use it for its own columns with custom
wxDataViewCtrl models.

interface/wx/dataview.h

@@ -1797,6 +1797,7 @@ enum wxDataViewCellRenderState
     There is a number of ready-to-use renderers provided:
     - wxDataViewTextRenderer,
     - wxDataViewIconTextRenderer,
+    - wxDataViewCheckIconTextRenderer,
     - wxDataViewToggleRenderer,
     - wxDataViewProgressRenderer,
     - wxDataViewBitmapRenderer,
@@ -2059,6 +2060,7 @@ public:
     wxDataViewIconText can be converted to and from a wxVariant using the left
     shift operator.
 
+    @see wxDataViewCheckIconTextRenderer
     @library{wxadv}
     @category{dvc}
 */
@@ -2081,6 +2083,58 @@ public:
 };
 
 
+/**
+    This renderer class shows a checkbox in addition to the icon and text shown
+    by the base class and also allows the user to toggle this checkbox.
+
+    By default this class doesn't allow the user to put the checkbox into the
+    third, i.e. indeterminate, state, even though it can display the state if
+    the program returns the corresponding value from the associated model. Call
+    Allow3rdStateForUser() explicitly if the user should be able to select the
+    3rd state interactively too.
+
+    This class is used internally by wxTreeListCtrl, and can be seen in action
+    in the corresponding sample.
+
+    @see wxDataViewIconTextRenderer, wxDataViewToggleRenderer
+    @library{wxadv}
+    @category{dvc}
+    @since 3.1.1
+ */
+class wxDataViewCheckIconTextRenderer : public wxDataViewRenderer
+{
+public:
+    static wxString GetDefaultType() { return wxS("wxDataViewCheckIconText"); }
+
+    /**
+        Create a new renderer.
+
+        By default the renderer is activatable, i.e. allows the user to toggle
+        the checkbox.
+     */
+    explicit wxDataViewCheckIconTextRenderer
+             (
+                  wxDataViewCellMode mode = wxDATAVIEW_CELL_ACTIVATABLE,
+                  int align = wxDVR_DEFAULT_ALIGNMENT
+             );
+
+    /**
+        Allow the user to interactively select the 3rd state for the items
+        rendered by this object.
+
+        As described in the class overview, this renderer can always display
+        the 3rd ("indeterminate") checkbox state if the model contains cells
+        with wxCHK_UNDETERMINED value, but it doesn't allow the user to set it
+        by default. Call this method to allow this to happen.
+
+        @param allow If @true, interactively clicking a checked cell switches
+            it to the indeterminate value and clicking it again unchecks it.
+            If @false, clicking a checked cell switches to the unchecked value,
+            skipping the indeterminate one.
+     */
+    void Allow3rdStateForUser(bool allow = true);
+};
+
 
 /**
     @class wxDataViewProgressRenderer
@@ -2140,6 +2194,7 @@ public:
 
     This class is used by wxDataViewCtrl to render toggle controls.
 
+    @see wxDataViewCheckIconTextRenderer
     @library{wxadv}
     @category{dvc}
 */