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

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

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.

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>