feat(input): add clearInputIcon property (#29246)

Issue number: resolves #26974

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## What is the current behavior?
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In https://github.com/ionic-team/ionic-framework/pull/26354 we updated
the clear icon to use an ionicon instead of an hardcoded SVG. This has
made it challenging to customize the icon.

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

- Added `clearInputIcon` property to allow developers to customize the
ionicon used.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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