Add wxControl::GetSizeFromTextSize() to size the control to its text.

This function can be used to size a, say, wxTextCtrl to be exactly of the size
needed to enter the given amount of text in it.

This patch adds wxGTK implementation for wxTextCtrl, wxChoice and wxCombobox;
changes to the samples and the documentation.

Closes #14812.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72935 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/control.h

@@ -152,6 +152,47 @@ public:
     */
     wxString GetLabelText() const;
 
+    /**
+        Determine the size needed by the control to leave the given area for
+        its text.
+
+        This function is mostly useful with control displaying short amounts of
+        text that can be edited by the user, e.g. wxTextCtrl, wxComboBox,
+        wxSearchCtrl etc. Typically it is used to size these controls for the
+        maximal amount of input they are supposed to contain, for example:
+        @code
+            // Create a control for post code entry.
+            wxTextCtrl* postcode = new wxTextCtrl(this, ...);
+
+            // And set its initial and minimal size to be big enough for
+            // entering 5 digits.
+            postcode->SetInitialSize(
+                postcode->GetSizeFromTextSize(
+                    postcode->GetTextExtent("99999")));
+        @endcode
+
+        Currently this method is only implemented for wxTextCtrl, wxComboBox
+        and wxChoice in wxGTK.
+
+        @param xlen The horizontal extent of the area to leave for text, in
+            pixels.
+        @param ylen The vertical extent of the area to leave for text, in
+            pixels. By default -1 meaning that the vertical component of the
+            returned size should be the default height of this control.
+        @return The size that the control should have to leave the area of the
+            specified size for its text. May return wxDefaultSize if this
+            method is not implemented for this particular control under the
+            current platform.
+
+        @since 2.9.5
+     */
+    wxSize GetSizeFromTextSize(int xlen, int ylen = -1) const;
+
+    /**
+        @overload
+    */
+    wxSize GetSizeFromTextSize(const wxSize& tsize) const;
+
     /**
         Sets the control's label.