add tests for accessing core type fields hidden behind anons

tests/unit/src/unitstd/AnonFieldAccess.unit.hx

@@ -0,0 +1,11 @@
+([1]:Iterable<Int>).iterator().next() == 1;
+([1]:{function shift ():Null<Int>;}).shift() == 1;
+([1]:{function pop ():Null<Int>;}).pop() == 1;
+([]:{function push (x:Int):Int;}).push(1) == 1;
+([1,2]:{function join (s:String):String;}).join(",") == "1,2";
+([1,2]:{function filter (s:Int->Bool):Array<Int>;}).filter(function (x) return x == 1).length == 1;
+([1]:{function map <T>(s:Int->T):Array<T>;}).map(function (x) return x+1)[0] == 2;
+("a":{function toUpperCase ():String;}).toUpperCase() == "A";
+("A":{function toLowerCase ():String;}).toLowerCase() == "a";
+
+