fix(VStepperVertical): provide eager in defaults props

[SonTT19]

Description

fixes #20025

Markup:

<template>
  <v-stepper-vertical eager>
    <template v-slot:default="{ step }">
      <v-stepper-vertical-item
        :complete="step > 1"
        subtitle="Personal details"
        title="Step one"
        value="1"
      >
        Lorem ipsum dolor sit amet consectetur adipisicing elit. Commodi,
        ratione debitis quis est labore voluptatibus! Eaque cupiditate minima,
        at placeat totam, magni doloremque veniam neque porro libero rerum unde
        voluptatem!

        <template v-slot:next="{ next }">
          <v-btn color="primary" @click="next"></v-btn>
        </template>

        <template v-slot:prev></template>
      </v-stepper-vertical-item>

      <v-stepper-vertical-item
        :complete="step > 2"
        subtitle="Contact Details"
        title="Step two"
        value="2"
      >
        Lorem ipsum dolor sit amet consectetur adipisicing elit. Commodi,
        ratione debitis quis est labore voluptatibus! Eaque cupiditate minima,
        at placeat totam, magni doloremque veniam neque porro libero rerum unde
        voluptatem!

        <template v-slot:next="{ next }">
          <v-btn color="primary" @click="next"></v-btn>
        </template>

        <template v-slot:prev="{ prev }">
          <v-btn variant="plain" @click="prev"></v-btn>
        </template>
      </v-stepper-vertical-item>

      <v-stepper-vertical-item
        subtitle="Confirmation"
        title="Step three"
        value="3"
        @click:next="onClickFinish"
      >
        Lorem ipsum dolor sit amet consectetur adipisicing elit. Commodi,
        ratione debitis quis est labore voluptatibus! Eaque cupiditate minima,
        at placeat totam, magni doloremque veniam neque porro libero rerum unde
        voluptatem!

        <template v-slot:next="{ next }">
          <v-btn color="primary" text="Finish" @click="next"></v-btn>
        </template>

        <template v-slot:prev="{ prev }">
          <v-btn v-if="!finished" variant="plain" @click="prev"></v-btn>

          <v-btn
            v-else
            text="Reset"
            variant="plain"
            @click="finished = false"
          ></v-btn>
        </template>
      </v-stepper-vertical-item>
    </template>
  </v-stepper-vertical>
</template>

<script>
  export default {
    data: () => ({
      finished: false,
    }),

    methods: {
      onClickFinish() {
        this.finished = true

        alert('Finished')
      },
    },
  }
</script>