Updates to Unicode files to Unicode 16, adjusts tests, and the
scripts used to parse UCD, to adapt to minor formatting differences
in UCD 16.
The `GenerateTest26.py` and `GenerateCommon.py` had a regexp to
extract properties from the `ScriptExtensions.txt` file. Previously,
all property lines had one space after space-separated list of scripts.
In UCD-16, this list is adjusted with right-padding, which throws off
the parser.
This commit adjusts the regexps to ignore padding spaces.
Starting with Unicode 15, the provided DerivedBidiClass data file
reports different default values to use for unassigned characters
in different groups.
Process the additional hints for that specific file, and allow
overriding the values later if more specific.
Since that was previously forbidden, change get_other_case() to
report when no valid value could be provided and allow skipping
conflicting rule lines that required that restriction.
While at it, Allow using the long identifiers in `ucptest` with
the `find bidi` command (underscores also allowed).
