docs(input, searchbar, textarea): improve docs for managing focus (#28614)

Issue number: Related to #18132 

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## What is the current behavior?
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The documentation about the `autofocus` prop is unclear and does not
accurately reflect how it actually works across browsers and devices.

## What is the new behavior?
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this PR. -->

- The documentation for `autofocus` and `setFocus` are more detailed.
- The documentation links to the relevant page in the docs.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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screenshots of how the component looks before and after the change. -->