[3.13] gh-104855: Update Tkinter tests for Tcl/Tk 8.7 and 9.0 (GH-120824) (GH-120864)

The tests are now passed with the current version of Tcl/Tk under
development (8.7b1+ and 9.0b3+).

The following changes were also made to make the tests more flexible:

* Helper methods like checkParam() now interpret the expected error message
  as a regular expression instead of a literal.
* Add support of new arguments in checkEnumParam():
  - allow_empty=True skips testing with empty string;
  - fullname= specifies the name for error message if it differs from the
    option name;
  - sort=True sorts values for error message.
* Add support of the allow_empty argument in checkReliefParam():
  allow_empty=True adds an empty string to the list of accepted values.
* Attributes _clip_highlightthickness, _clip_pad and  _clip_borderwidth
  specify how negative values of options -highlightthickness, -padx, -pady
  and -borderwidth are handled.
* Use global variables for some common error messages.

(cherry picked from commit 6ad26de6e8)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Lib/test/test_tkinter/test_variables.py

@@ -6,7 +6,7 @@ import tkinter
 from tkinter import (Variable, StringVar, IntVar, DoubleVar, BooleanVar, Tcl,
                      TclError)
 from test.support import ALWAYS_EQ
-from test.test_tkinter.support import AbstractDefaultRootTest
+from test.test_tkinter.support import AbstractDefaultRootTest, tcl_version
 
 
 class Var(Variable):
@@ -112,6 +112,8 @@ class TestVariable(TestBase):
         self.assertTrue(v.side_effect)
 
     def test_trace_old(self):
+        if tcl_version >= (9, 0):
+            self.skipTest('requires Tcl version < 9.0')
         # Old interface
         v = Variable(self.root)
         vname = str(v)