fix(layout): use suspense to delay render of layout items

[nekosaur]

Description

closes #15202

same principle as in #15215

Motivation and Context

How Has This Been Tested?

Markup:

<template>
  <v-app>
    <v-navigation-drawer permanent>
      nav drawer

    </v-navigation-drawer>
    <v-app-bar>
      <v-toolbar-title>Title</v-toolbar-title>
    </v-app-bar>

    <v-main app>
      <v-container>
        Something!
      </v-container>
    </v-main>
  </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 features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and backwards compatible changes and next for non-backwards compatible changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)

[KaelWD]

There's still vuejs/core#6095, I haven't seen it in this PR but I also have no idea why it happens in the first place.

[johnleider]

Is there a reason for naming it layoutReady instead of isReady?

Everything else looks good.

[warflash]

Any news on when we'll see this one merged? 🙏

[KaelWD]

When vuejs/core#6095 is.

The base branch was changed.