bpo-34829: Add missing selection_ methods to the Tkinter Spinbox. (GH-9617)

Implement the methods selection_from(), selection_range(), selection_present()
and selection_to() for Tkinter Spinbox.
diff --git a/Doc/whatsnew/3.8.rst b/Doc/whatsnew/3.8.rst
index a146249..d9c3f1b 100644
--- a/Doc/whatsnew/3.8.rst
+++ b/Doc/whatsnew/3.8.rst
@@ -167,6 +167,16 @@
 post-handshake authentication.
 (Contributed by Christian Heimes in :issue:`34670`.)
 
+tkinter
+-------
+
+Added methods :meth:`~tkinter.Spinbox.selection_from`,
+:meth:`~tkinter.Spinbox.selection_present`,
+:meth:`~tkinter.Spinbox.selection_range` and
+:meth:`~tkinter.Spinbox.selection_to`
+in the :class:`tkinter.Spinbox` class.
+(Contributed by Juliette Monsel in :issue:`34829`.)
+
 venv
 ----