[String] CJK Grapheme breaking fast-paths for fullwidth

[milseman]

Add in grapheme breaking fast-paths for fullwidth forms and
punctuation. Extend non-combining kana fast-paths to include vowel
extender.

Replace this paragraph with a description of your changes and rationale. Provide links to external references/discussions if appropriate.

[milseman]

@swift-ci please test and merge

[milseman]

@swift-ci please benchmark

[swift-ci]

Build comment file:

Performance: -O

TEST	OLD	NEW	DELTA	RATIO
Regression
StringEqualPointerComparison	538	589	+9.5%	0.91x (?)

Performance: -Osize

TEST	OLD	NEW	DELTA	RATIO
Regression
StringEqualPointerComparison	512	564	+10.2%	0.91x
Improvement
EqualStringSubstring	11	10	-9.1%	1.10x

How to read the data

The tables contain differences in performance which are larger than 8% and differences in code size which are larger than 1%.

If you see any unexpected regressions, you should consider fixing the
regressions before you merge the PR.

Noise: Sometimes the performance results (not code size!) contain false
alarms. Unexpected regressions which are marked with '(?)' are probably noise.
If you see regressions which you cannot explain you can try to run the
benchmarks again. If regressions still show up, please consult with the
performance team (@eeckstein).

Hardware Overview

  Model Name: Mac Pro
  Model Identifier: MacPro6,1
  Processor Name: 8-Core Intel Xeon E5
  Processor Speed: 3 GHz
  Number of Processors: 1
  Total Number of Cores: 8
  L2 Cache (per Core): 256 KB
  L3 Cache: 25 MB
  Memory: 64 GB

--------------

[milseman]

Ugh, the corresponding benchmarks are disabled. Need to also clean them all up.