fix(VMenu): apply position:relative to v-app

[Tofandel]

Description

fixes #13821

Motivation and Context

All the calculations assume the v-app was relatively positioned, except it wasn't, only the v-application--wrap was relatively positioned leading to the demonstrated bug

How Has This Been Tested?

Visually

Markup:

// Paste your FULL Playground.vue here

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.