Upgrade to Unicode 15.0.0

[syvb]

Unicode 15 will be released tomorrow on Sept. 13. This updates the Unicode tables to the latest version.

Change notes:

• The {Grapheme,Word,Sentence}BreakTest.txt files are unchanged (except for the file header), so no change is needed to testdata.rs
• Changes to UAX#29 (Unicode Text Segmentation):
  • Revision 41 doesn't make any substantive changes
  • Revision 40 adds "four postbase Kawi characters to the SpacingMark exceptions" (U+11F03, U+11F34, U+11F35, U+11F41). Currently it looks like none of the 24 SpacingMark exceptions are implemented (although the impact of this is very minor, it only affects word breaking in extended mode), so this should be fixed in a separate PR

[Manishearth]

Thanks! File a followup about the exceptions?