fix(VAvatar): add style for start, end props same as VIcon

[SonTT19]

Description

fixes #19349

Markup:

<template>
  <div>
    <div>
      <v-avatar color="blue-darken-2" start>
        <v-icon icon="mdi-alarm" />
      </v-avatar>
      Username
      <v-avatar color="blue-darken-2" end>
        <v-icon icon="mdi-alarm" />
      </v-avatar>
    </div>
    <div>
      <v-avatar color="blue-darken-2">
        <v-icon icon="mdi-alarm" />
      </v-avatar>
      Username
      <v-avatar color="blue-darken-2">
        <v-icon icon="mdi-alarm" />
      </v-avatar>
    </div>

    <div>
      <v-avatar color="blue-darken-2" end start>
        <v-icon icon="mdi-alarm" />
      </v-avatar>
      Username
      <v-avatar color="blue-darken-2" end start>
        <v-icon icon="mdi-alarm" />
      </v-avatar>
    </div>
  </div>
</template>