st.c: use power-of-two sizes to avoid slow modulo ops

* st.c (hash_pos): use bitwise AND to avoid slow modulo op
  (new_size): power-of-two sizes for hash_pos change
  (st_numhash): adjust for common keys due to lack of prime modulo
  [Feature #9425]
* hash.c (rb_any_hash): right shift for symbols
* benchmark/bm_hash_aref_miss.rb: added to show improvement
* benchmark/bm_hash_aref_sym_long.rb: ditto
* benchmark/bm_hash_aref_str.rb: ditto
* benchmark/bm_hash_aref_sym.rb: ditto
* benchmark/bm_hash_ident_num.rb: added to prevent regression
* benchmark/bm_hash_ident_obj.rb: ditto
* benchmark/bm_hash_ident_str.rb: ditto
* benchmark/bm_hash_ident_sym.rb: ditto

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45384 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

benchmark/bm_hash_aref_str.rb

@@ -0,0 +1,4 @@
+h = {}
+strs = ('a'..'z').to_a.map!(&:freeze)
+strs.each { |s| h[s] = s }
+200_000.times { strs.each { |s| h[s] } }