feat: add clear button to search bar that follows theme colors

[rosvik]

PR Creator Checklist

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• You've discussed making your changes with a member of the dev team per contributing rules in the README
  • See (x) Button in search-bar barely visible in dark mode #597
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  • There are however some errors other places that are not touched by this PR
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Summary

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closes #597

• Adds a custom clear button to SearchBox that follows theme colors, in favor of the native one. I tried to keep it functionally identical to the native implementation, but couldn't find a SF icon with a solid background, so that might be the only significant difference.
• Adds some hitSlop to the clear button and the search field, to make it easier hit.

Screenshots

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Simulator.Screen.Recording.-.iPhone.14.-.2023-07-26.at.22.26.29.mp4

Test Plan

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Functionality shown in recording above ^