vue-cli/packages/@vue/cli-service/lib/commands/build/demo-wc.html

<title><%- htmlWebpackPlugin.options.libName %> demo</title>
<script src="https://unpkg.com/vue"></script>
<script src="./<%- htmlWebpackPlugin.options.libName %>.js"></script>

<% for (const comp of htmlWebpackPlugin.options.components) { %>
<<%= comp %>></<%= comp %>>
<% } %>