Use character classes for ID in the lexer

Author: steve-s

com.oracle.truffle.r.parser/src/com/oracle/truffle/r/parser/ParserGeneration.java

@@ -105,5 +105,6 @@ public class ParserGeneration {
         "allow 'function(...=NULL)', which has no effect, but also causes not error in GNU-R",
         "report tokens and other metadata to the code builder",
         "convert to ANTLR4",
+        "use character classes instead of character sets in lexer"
     };
 }

com.oracle.truffle.r.parser/src/com/oracle/truffle/r/parser/R.g

@@ -954,7 +954,7 @@ fragment OP_NAME
     | ('*'|'/'|'+'|'-'|'>'|'<'|'='|'|'|'&'|':'|'^'|'.'|'~'|','|'?')
     ;
 
-fragment ID_NAME : ('a'..'z'|'A'..'Z'|'α'..'ω'|'Α'..'Ω'|'_') ('a'..'z'|'A'..'Z'|'0'..'9'|'α'..'ω'|'Α'..'Ω'|'_'|'.')* ;
+fragment ID_NAME : [\p{Alpha}_] [\p{Alnum}_.]* ;
 
 fragment ESC_SEQ
     : '\\' ('b'|'t'|'n'|'f'|'r'|'"'|'\''|'`'|'\\'|' '|'a'|'v')