fix(VTextField): show label slot when filled prop is used

[KaelWD]

fixes #11533
see vuejs/vue#11714

Does this break anything? Is there some way setLabelWidth would need to be called before the watcher is set up?

Markup:

<template>
  <v-container>
    <v-text-field filled>
      <template #label><span>#Slot label</span></template>
    </v-text-field>

    <v-text-field filled>
      <template slot="label"><span>Slot label</span></template>
    </v-text-field>

    <v-text-field filled label="Prop label" />
  </v-container>
</template>

[johnleider]

Do you intent to leave this or just remaining dev code?

[KaelWD]

Intended, can remove though if you like

[johnleider]

I don't see anything that this would obviously break.