refactor: convert v-avatar to typescript

[jacekkarczmarczyk]

How Has This Been Tested?

manually

Markup:

<template>
  <v-app dark>
    <v-content>
      <v-container>
        <v-layout align-center justify-space-around wrap>
          <v-avatar color="indigo">
            <v-icon dark>account_circle</v-icon>
          </v-avatar>

          <v-avatar>
            <img src="https://cdn.vuetifyjs.com/images/john.jpg" alt="John">
          </v-avatar>

          <v-badge overlap>
            <span slot="badge">3</span>
            <v-avatar color="purple red--after">
              <v-icon dark>notifications</v-icon>
            </v-avatar>
          </v-badge>

          <v-avatar color="teal">
            <span class="white--text headline">C</span>
          </v-avatar>

          <v-avatar color="red">
            <span class="white--text headline">J</span>
          </v-avatar>
        </v-layout>
      </v-container>
    </v-content>
  </v-app>
</template>

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any feature but make things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes, dev for new features and breaking changes).
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have created a PR in the documentation with the necessary changes.

[codecov]

Codecov Report

Merging #4538 into master will increase coverage by 0.17%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #4538      +/-   ##
=========================================
+ Coverage   89.53%   89.7%   +0.17%     
=========================================
  Files         206     207       +1     
  Lines        4884    4956      +72     
  Branches     1236    1255      +19     
=========================================
+ Hits         4373    4446      +73     
+ Misses        411     410       -1     
  Partials      100     100

Impacted Files	Coverage Δ
src/components/VAvatar/index.ts	100% <ø> (ø)
src/components/VAvatar/VAvatar.ts	100% <100%> (ø)
src/components/VApp/VApp.js	100% <0%> (ø)	⬆️
src/components/Vuetify/index.ts	100% <0%> (ø)	⬆️
src/components/VApp/mixins/app-breakpoint.js	100% <0%> (ø)
src/components/VToolbar/VToolbar.js	96.72% <0%> (+1.63%)	⬆️

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[iabdulin]

The 200 millionth pull request!
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