feat(filters): revert filter being restricted to top level

See: 5bcea64

Closes dart-archive#758

Author: mhevery

lib/core/parser/dynamic_parser_impl.dart

@@ -210,7 +210,7 @@ class DynamicParserImpl {
 
   parsePrimary() {
     if (optionalCharacter($LPAREN)) {
-      var result = parseExpression();
+      var result = parseFilter();
       expectCharacter($RPAREN);
       return result;
     } else if (peek.isKeywordNull || peek.isKeywordUndefined) {

test/core/parser/parser_spec.dart

@@ -987,6 +987,12 @@ main() {
         expect(eval("1|increment:2", filters)).toEqual(3);
       });
 
+      it('should evaluate grouped filters', () {
+        context = {'name': 'MISKO'};
+        expect(eval('n = (name|lowercase)', filters)).toEqual('misko');
+        expect(eval('n')).toEqual('misko');
+      });
+
       it('should parse filters', () {
         expect(() {
           eval("1|nonexistent");