Changes 14: Model prop fixes

[bastianallgeier]

This PR …

• 🚨 Merge first: Changes 1: Refactor content storage to use new VersionId class #6436
• 🚨 Merge first: Changes 2: Plain Text Handler Refactoring #6439
• 🚨 Merge first: Changes 3: New Version class #6442
• 🚨 Merge first: Changes 4: Refactor PlainTextContentStorageHandler to use Language object #6448
• 🚨 Merge first: Changes 5: ContentStorageHandler Abstract #6449
• 🚨 Merge first: Changes 6: Version class improvements and unit tests #6450
• 🚨 Merge first: Changes 7: Move ContentStorage methods to ContentStorageHandler #6454
• 🚨 Merge first: Changes 8: New ModelWithContent::version method #6455
• 🚨 Merge first: Changes 9: Remove content storage class #6456
• 🚨 Merge first: Changes 10: New MemoryContentStorageHandler #6457
• 🚨 Merge first: Changes 11: Language::ensure & Languages::ensure #6483
• 🚨 Merge first: Changes 12: More Version class improvements #6490
• 🚨 Merge first: Changes 13: New translation classes #6491

Reasoning

Our Models run parent::__construct before setting their props. This leads to a situation where ::setContent and ::setTranslations cannot access vital properties, such as isDraft, slug, id etc. because they are not available yet. We cannot properly switch to the Version implementation as long as this is not fixed.

Refactoring

• Page::__construct calls parent::__construct after setting the props
• Site::__construct calls parent::__construct after setting the props
• User::__construct calls parent::__construct after setting the props
• File::__construct calls parent::__construct after setting the props

Breaking changes

None expected

Ready?

• In-code documentation (wherever needed)
• Unit tests for fixed bug/feature
• Tests and CI checks all pass

For review team

• Add changes & docs to release notes draft in Notion