docs: Update $props documentation to clarify when prop values are deeply re…

[BernieSumption]

This PR updates the $props documentation to clarify when prop values are deeply reactive

In particular, this wording confused me:

Fallback values are not turned into reactive state proxies

As I took it to be an exception, implying that non-fallback values are turned into reactive state proxies. Some experimentation revealed that this is not the case.

Side note: this is my first contribution, I'm new to svelte and reading a lot of docs and happy to help improve them where I'm able. If it would be preferable to discuss docs improvements before opening a PR, please let me know where best to open the discussion.

Before submitting the PR, please make sure you do the following

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• [✓] Prefix your PR title with feat:, fix:, chore:, or docs:.
• [✓] This message body should clearly illustrate what problems it solves.
• [n/a] Ideally, include a test that fails without this PR but passes with it.

Tests and linting

• [✓] Run the tests with pnpm test and lint the project with pnpm lint

[changeset-bot]

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Latest commit: 549826a

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[pkg-pr-new]

pnpm add https://pkg.pr.new/svelte@13994

commit: 549826a

[dummdidumm]

thank you!