[SwiftSyntax] Add convenience initializer for BinaryOperatorExpr

Author: kimdv

utils/gyb_syntax_support/protocolsMap.py

@@ -22,5 +22,8 @@
     'StmtBuildable': [
         'CodeBlockItem',
         'SyntaxBuildable'
+    ],
+    'TokenSyntax': [
+        'BinaryOperatorExpr'
     ]
 }