Don't convert unbound method to proc in Truffle::Splitter.split

Author: andrykonchin

src/main/ruby/truffleruby/core/splitter.rb

@@ -107,7 +107,7 @@ def split_type_chars(string, limit, callable)
 
           callable.call(last)
         else
-          string.each_char(&callable)
+          string.each_char { |c| callable.call(c) }
 
           callable.call(empty_string(string)) if tail_empty?(limit)
         end