fix(input, textarea, select): reduce padding on slotted buttons (#28676)

Issue number: N/A

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## What is the current behavior?
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Buttons slotted in the start/end slots of input, textarea, or select
have a lot of excess padding that can cause them to look misaligned from
other pieces such as the control's label, especially when using
`fill="clear"`.

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

Padding removed, and a border radius added so that non-clear buttons as
well as the focus state on clear buttons still look okay. Existing
screenshot tests have also been updated to include buttons (non-clear
ones so you can see the border radius in the screenshots).

Let me know if you think this should go on a feature branch instead. I
chose `main` because the current experience looks somewhat broken and we
just did a minor release recently, but this could be considered a
notable enough behavior change.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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and migration path for existing applications below. -->


## Other information

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

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Co-authored-by: ionitron <hi@ionicframework.com>