Add .sync modifier to v-bind directive

[maurop123]

What problem does this feature solve?

Currently, this syntax is supported,

<component v-bind="{propA, propB}" />

However, if you want to use the .sync modifier on the props, then you can't use the ES6 object destructuring syntax anymore.

<component :propA.sync="propA" :propB.sync="propB" />

What does the proposed API look like?

<component v-bind.sync="{propA, propB}" />