Add test

Author: shulhi

jscomp/test/VariantCoercion.js

@@ -120,3 +120,9 @@ module CoerceFromPolyvariantToVariant = {
   let withUnboxedCatchAll: withUnboxedCatchAll = #One
   let withUnboxedCatchAllP = (withUnboxedCatchAll :> withUnboxedCatchAllP)
 }
+
+module CoerceVariantBinaryOp = {
+  type flag = | @as(0) A | @as(2) B
+
+  let x = 0->lor((B :> int))
+}