Make EmbedBuilder$setDescription overrideable

[Currypan1229]

Pull Request Etiquette

• [x] I have checked the PRs for upcoming features/bug fixes.
• [x] I have read the contributing guidelines.

Changes

• [x] Internal code
• [ ] Library interface (affecting end-user code)
• [ ] Documentation
• [ ] Other: _____

Closes Issue: NaN

Description

This allows developers to override the method.