feat($theme-default) Propagate toggleSidebar event to parent

[shortdiv]

Summary
The toggleSidebar event was not being propagated up from the NavBar component. This PR emits that event up to parent elements, so applications have access to the state of whether the side bar is open.

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Build-related changes
• Other, please describe:

If changing the UI of default theme, please provide the before/after screenshot:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

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• Firefox
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• IE

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature
• Related documents have been updated
• Related tests have been updated

To avoid wasting your time, it's best to open a feature request issue first and wait for approval before working on it.

Other information:

[kefranabg]

Hi @shortdiv,

Why would you need to do catch this event? Could you provide a concrete example?

[shortdiv]

Hey! Sure thing! It seems that the body of the docs content scrolls even when the sidebar is open, which makes for a pretty janky experience. If the toggle sidebar state is bubbled up, you can easily add and remove an overflow property to the body via the layout component.

<template>
  <Layout @toggle-sidebar="controlBodyScroll">
    ...
  </Layout>
</template>
<script>
import Layout from "@parent-theme/layouts/Layout.vue";

export default {
  components: { Layout },
  methods: {
    controlBodyScroll(isSidebarOpen) {
      if (!isSidebarOpen) {
        document.body.style.overflow = "hidden";
      } else {
        document.body.style.overflow = "auto";
      }
    }
  }
}
</script>

[vue-bot]

Hey @shortdiv, thank you for your time and effort spent on this PR, contributions like yours help make Vue better for everyone. Cheers! 💚