Components: migrate SearchControl to SCSS module

[im3dabasia]

What?

Part of: #66806

Migrates SearchControl from Emotion (@emotion/styled) to an SCSS module.

Why?

The @wordpress/components package is moving off Emotion (CSS-in-JS) to SCSS modules to reduce runtime bundle size and execution cost, remove dev-tools class pollution, and avoid iframe/portal styling issues. SearchControl only has two static styled wrappers, making it a low-risk component to migrate.

How?

• Replaced the StyledInputControl = styled( InputControl ) and StyledIcon = styled( Icon ) definitions in styles.ts with .input and .icon classes in a new style.module.scss.
• Rendered plain InputControl and Icon with the module classes instead of the styled components.
• Merged the .input class into the existing clsx on InputControl so the pre-existing components-search-control class and any consumer-passed className are preserved.
• Deleted the now-unused styles.ts.

No public API, class name, or behavior changes.

Testing Instructions

1. Open a view that renders a SearchControl (e.g. Storybook → Components → SearchControl, or the block inserter / global styles search fields).
2. Confirm the search input renders correctly and the native WebKit search decorations/clear button remain hidden.
3. Confirm the search icon renders and is horizontally flipped in LTR (and appears normally in RTL).
4. Type a query and clear it; confirm behavior is unchanged.

Use of AI Tools

This PR was authored with the assistance of Claude Code (Anthropic). All generated changes were reviewed, tested, and verified by me.

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Co-authored-by: im3dabasia <im3dabasia1@git.wordpress.org>
Co-authored-by: mirka <0mirka00@git.wordpress.org>

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[mirka]

Looks good, please add a changelog before merge 🙏 (also).