folly: Range: implement find_first_of and optimize qfind(Range, char)

folly: Range: implement find_first_of and optimize qfind(Range, char)

Summary:
implement ##find_first_of## and optimize ##Range.find(char)##

============================================================================
folly/test/RangeBenchmark.cpp                   relative  time/iter  iters/s
============================================================================
LongFindSingleCharDirect                                     2.76ms   362.63
LongFindSingleCharRange                           15.88%    17.37ms    57.58
ShortFindSingleCharDirect                                   53.41fs   18.72T
ShortFindSingleCharRange                           0.00%    29.22ns   34.22M
============================================================================

Test Plan:
- added new tests

- ran all folly tests

fbconfig -r folly/ && mkk runtests_opt

Reviewed By: tudorb@fb.com

FB internal diff: D576720