Support propsData

[lmiller1990]

I am moving a small code base to VTU v2. One of the main breaking changes is the change from propsData -> props in the mounting options.

Eg:

// VTU v1

const A = {
  props: ['msg']
}

mount(A, {
  propsData: { msg: 'msg' }
})

// VTU v2

mount(A, {
  props: { msg: 'msg' }
})

I'd like to allow propsData to work as well. I'd suggest we support both for migration purposes. We won't document propsData, since using props matches the props key in Vue components, but we will keep both for convenience.

The acceptance criteria for this PR are as follows:

• support the propsData mounting method
• pass whatever is received from propsData to props in src/mount.ts
• add at least one tests with propsData