Use the image object in snippets

[gagarine]

Describe the PR

Use the image object in snippets. This allow direct access to resize() and other image functions.

Related issues

The current code confuses peoples. See https://forum.getkirby.com/t/new-editor-referencing-image-metadata/15905/5?u=gagarine

• Fixes #

Ready?

• [ ] Added unit tests for fixed bug/feature
• [ ] Passing all unit tests
• [ ] Fixed code style issues with CS fixer and composer fix
• [ ] Added in-code documentation (if needed)