[BUG] Null characters do not work in regular expression character classes

[anthony-chang]

Describe the bug
We will fallback to CPU for null characters inside a character class.

Steps/Code to reproduce bug
Run any regular expression with \u0000 inside a character class.

Expected behavior

• Do not throw unsupported exception for null characters in character classes, and transpile them to the octal/hex representation
• Add \u0000 to the predefined classes \p{ASCII} and \p{Cntrl}
• Update compatibility docs

Environment details (please complete the following information)
N/A

Additional context
Depends on rapidsai/cudf#11112
Related to #5834