Fix clustering of gc=Cf, GCB=CN codepoints

[lhecker]

• Previously we would mark all gc=Cf (Control, format) codepoints
  as zero-width, but that ignores that the majority of them are also
  GCB=CN (Control = does not join), which meant we ended up with
  zero-width grapheme clusters. Those cannot exist under a terminal.
  So, this PR makes all gc=Cf, GCB=CN codepoints zero-width, but also
  treats them as Extender codepoints, which mirrors wcswidth.
• This PR also updates the tables to Unicode 16.0.
• Finally, there's a minor code cleanup of the generator.

Closes #18267

Validation Steps Performed

• Unit tests ✅
• Thai does not have random gaps anymore due to ZWSP ✅

[DHowett]

oh no. i now realize that conhost may have expected these to be Ambiguous - in applications that target CJK and do box drawing. i can't remember...