Refactor is_logged_out conditions in super sidebar user-bar

From: !130629 (comment 1548750135)

Multiple instances of this.sidebarData.is_logged_in conditions for rendering content in <user-bar> add complexity and make it confusing to know how content should react to different states.

There's an opportunity to refine at what level we conditionally render content e.g. rather than nested conditions:

<template>
  <div>
    <div v-if="condition"></div>
    <div>
      <div v-if="condition"></div>
      <div v-else></div>
    </div>
  </div>
</template>

Split content into top level logged-in/logged-out user bar content

<template>
  <div v-if="condition"></div>
  <div v-else></div>
</template>

Alternatively we could create <user-bar-logged-out> if it make it simpler with less duplication of styles/functionality.