bpo-43013: Fix old tkinter module names in idlelib (GH-24326)

Lowercase 'tkColorChooser', 'tkFileDialog', 'tkSimpleDialog', and
'tkMessageBox' and remove 'tk'.  Just lowercase 'tkFont' as 'font'
is already used.  Adjust import.
diff --git a/Lib/idlelib/pyshell.py b/Lib/idlelib/pyshell.py
index abe8a85..0407ca9 100755
--- a/Lib/idlelib/pyshell.py
+++ b/Lib/idlelib/pyshell.py
@@ -21,13 +21,13 @@
     except (ImportError, AttributeError, OSError):
         pass
 
-import tkinter.messagebox as tkMessageBox
+from tkinter import messagebox
 if TkVersion < 8.5:
     root = Tk()  # otherwise create root in main
     root.withdraw()
     from idlelib.run import fix_scaling
     fix_scaling(root)
-    tkMessageBox.showerror("Idle Cannot Start",
+    messagebox.showerror("Idle Cannot Start",
             "Idle requires tcl/tk 8.5+, not %s." % TkVersion,
             parent=root)
     raise SystemExit(1)
@@ -261,7 +261,7 @@ def store_file_breaks(self):
         except OSError as err:
             if not getattr(self.root, "breakpoint_error_displayed", False):
                 self.root.breakpoint_error_displayed = True
-                tkMessageBox.showerror(title='IDLE Error',
+                messagebox.showerror(title='IDLE Error',
                     message='Unable to update breakpoint list:\n%s'
                         % str(err),
                     parent=self.text)
@@ -771,7 +771,7 @@ def runcode(self, code):
                 exec(code, self.locals)
         except SystemExit:
             if not self.tkconsole.closing:
-                if tkMessageBox.askyesno(
+                if messagebox.askyesno(
                     "Exit?",
                     "Do you want to exit altogether?",
                     default="yes",
@@ -805,7 +805,7 @@ def write(self, s):
         return self.tkconsole.stderr.write(s)
 
     def display_port_binding_error(self):
-        tkMessageBox.showerror(
+        messagebox.showerror(
             "Port Binding Error",
             "IDLE can't bind to a TCP/IP port, which is necessary to "
             "communicate with its Python execution server.  This might be "
@@ -816,7 +816,7 @@ def display_port_binding_error(self):
             parent=self.tkconsole.text)
 
     def display_no_subprocess_error(self):
-        tkMessageBox.showerror(
+        messagebox.showerror(
             "Subprocess Connection Error",
             "IDLE's subprocess didn't make connection.\n"
             "See the 'Startup failure' section of the IDLE doc, online at\n"
@@ -824,7 +824,7 @@ def display_no_subprocess_error(self):
             parent=self.tkconsole.text)
 
     def display_executing_dialog(self):
-        tkMessageBox.showerror(
+        messagebox.showerror(
             "Already executing",
             "The Python Shell window is already executing a command; "
             "please wait until it is finished.",
@@ -945,7 +945,7 @@ def get_warning_stream(self):
 
     def toggle_debugger(self, event=None):
         if self.executing:
-            tkMessageBox.showerror("Don't debug now",
+            messagebox.showerror("Don't debug now",
                 "You can only toggle the debugger when idle",
                 parent=self.text)
             self.set_debugger_indicator()
@@ -1003,7 +1003,7 @@ def endexecuting(self):
     def close(self):
         "Extend EditorWindow.close()"
         if self.executing:
-            response = tkMessageBox.askokcancel(
+            response = messagebox.askokcancel(
                 "Kill?",
                 "Your program is still running!\n Do you want to kill it?",
                 default="ok",
@@ -1254,7 +1254,7 @@ def open_stack_viewer(self, event=None):
         try:
             sys.last_traceback
         except:
-            tkMessageBox.showerror("No stack trace",
+            messagebox.showerror("No stack trace",
                 "There is no stack trace yet.\n"
                 "(sys.last_traceback is not defined)",
                 parent=self.text)