feat(VSkeletonLoader): port to v3

[SteinRobert]

WIP

Description

Update v-skeleton-loader to v3. Discussing details on Discord

Motivation and Context

The skeleton loader should work for v3 too!

How Has This Been Tested?

Basically migrated v3.

1. Split into v-skeleton-loader and v-skeleton-loader-item
2. Update props
3. Update style for new structure (incl. margin-inline-start stuff for ltr/rtl)

Markup:

<template>
  <v-container>
    <div class="mb-3">
      <v-skeleton-bone type="heading" rounded/>
    </div>
    <div class="mb-3">
      <v-skeleton-bone type="subheading"/>
    </div>

    <div class="mb-3">
      <v-skeleton-bone type="image"/>
    </div>

    <div class="mb-3">
      <v-skeleton-bone type="text"/>
    </div>
  </v-container>
</template>

<script>
  export default {
    data: () => ({
    //
    }),
  }
</script>

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] 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:

• [x] The PR title is no longer than 64 characters.
• [x] 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).
• [x] 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)