Address feedback on platform-provided mixins explainer (1)

[anaskim]

Updates:

• Deleted paragraph on "behavior" vs "mixins". Will wait for more feedback on naming.
• Updated API shape to access attributes/properties.
• Added example to explore declarative version further.
• Added clarification and example workaround for dynamic attribute/mixins changes.
• Expanded section on the (future) possibility of conflicting mixins being used together and strategies to mitigate conflicts.

[anaskim]

Thanks for reviewing and merging!