bpo-38636: Fix IDLE tab toggle and file indent width (GH-17008)

These Format menu functions (default shortcuts Alt-T and Alt-U)
were mistakenly disabled in 3.7.5 and 3.8.0.
diff --git a/Lib/idlelib/editor.py b/Lib/idlelib/editor.py
index dff104f..92dcf57 100644
--- a/Lib/idlelib/editor.py
+++ b/Lib/idlelib/editor.py
@@ -186,8 +186,9 @@
         text.bind("<<uncomment-region>>", fregion.uncomment_region_event)
         text.bind("<<tabify-region>>", fregion.tabify_region_event)
         text.bind("<<untabify-region>>", fregion.untabify_region_event)
-        text.bind("<<toggle-tabs>>", self.Indents.toggle_tabs_event)
-        text.bind("<<change-indentwidth>>", self.Indents.change_indentwidth_event)
+        indents = self.Indents(self)
+        text.bind("<<toggle-tabs>>", indents.toggle_tabs_event)
+        text.bind("<<change-indentwidth>>", indents.change_indentwidth_event)
         text.bind("<Left>", self.move_at_edge_if_selection(0))
         text.bind("<Right>", self.move_at_edge_if_selection(1))
         text.bind("<<del-word-left>>", self.del_word_left)