Add another test for runtime order of template literals (#6092)

More proof that it really is unsafe to merge the .concat calls if the
value is an expression that has any chance of executing impure code 😢

packages/babel-plugin-transform-es2015-template-literals/test/fixtures/spec/order2/exec.js

@@ -0,0 +1,19 @@
+const calls = [];
+
+`
+  ${{
+    [Symbol.toPrimitive]() {
+      calls.push(1);
+      return "foo";
+    }
+  }}
+  ${1 +
+    {
+      valueOf() {
+        calls.push(2);
+        return 2;
+      }
+    }}
+`;
+
+assert.deepEqual(calls, [1, 2]);

packages/babel-plugin-transform-es2015-template-literals/test/fixtures/spec/order2/options.json

@@ -0,0 +1,3 @@
+{
+  "minNodeVersion": "6.0.0"
+}