docs: add note about object/array default values in defineModel

[whysopaul]

Description of Problem

The v-model/defineModel documentation does not mention that object/array literals should be avoided as default values, and that wrapped functions should be used instead.

Quote from Typing Component Props - Props Default Values:

Note that default values for mutable reference types (like arrays or objects) should be wrapped in functions when using withDefaults to avoid accidental modification and external side effects. This ensures each component instance gets its own copy of the default value. This is not necessary when using default values with destructure.

Proposed Solution

Add a short note using the text from the quote above in a warning block to the following sections:

1. Component v-model - Under the Hood
2. API Reference - defineModel()

Also note that, as when using withDefaults with defineProps, default values for mutable reference types (like arrays or objects) should be wrapped in functions in defineModel to avoid accidental modification and external side effects.

Additional Information

Since v-model uses props/emits under the hood, this will help highlight the connection between them.

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[bencodezen]

Thanks for the PR @whysopaul! I recommended two tweaks to the phrasing to make it more concise. Let me know if you have questions or want to discuss it further.

[whysopaul]

Hello @bencodezen! Thanks for the comments. I've applied the suggested changes.