Saxon Regular Expressions translator code used by Elemental

This is a slight modification of the regular expressions code from the package net.sf.saxon.functions.regex of Saxon-HE 9.4.0-9. The original code is Copyright Saxonica Limited and is released by them under the Mozilla Public License 1.1.

Thanks to Saxonica for the excellent Saxon.

This modified code is used by Elemental in its implementation of the XQuery functions: fn:analyze-string, fn:matches, fn:replace, and fn:tokenize.

The modifications:

1. change the package name of the classes (from net.sf.saxon.functions.regex to org.exist.thirdparty.net.sf.saxon.functions.regex),
2. added an MPL 1.1 license declaration to the files,
3. update the code for use with a newer Saxon dependency,
4. are released under the same Mozilla Public License 1.1.