Add a few more test cases

Author: shulhi

jscomp/test/VariantCoercion.js

@@ -125,4 +125,12 @@ module CoerceVariantBinaryOp = {
   type flag = | @as(0) A | @as(2) B
 
   let x = 0->lor((B :> int))
+
+  type flagStr = | @as("one") One | @as("two") Two
+
+  let y = (One :> string)->String.length
+
+  type flagFloat = | @as(1.5) X | @as(2.0) Y
+
+  let z = (X :> float) +. (Y :> float) +. 1.5
 }