Update Checkbox styling for mobile webview

[lilywuyanru]

WHY are these changes introduced?

Fixes https://github.com/Shopify/polaris-internal/issues/1580
Fixes #33786

Caution

Basing this PR off of #11896 (which is also based off #11837) and will not merge until that ships.

Figma link

Update checkbox styling for mobile webviews

• when breakpoint is below md, update border to 1px
• change customized icon to Polaris CheckIcon
• keeps 4px border radius
• when breakpoint is below md, change checkbox size from 18px to 20px

Unchecked

Before	After

Checked

Before	After

WHAT is this pull request doing?

How to 🎩

Tip

Make sure you have the breakpoint in storybook at sm or xs to see the changes

Before Storybook
After Storybook

🎩 checklist

• Tested a snapshot
  - [ ] Tested on mobile

[translation-platform]

Localization quality issues found

The following issues may affect the quality of localized translations if they are not addressed:

• The value Clear for key Polaris.ActionList.SearchField.clearButtonLabel is very short. Short strings are more likely to be misunderstood by translators without context. Please provide additional context for the translators if possible.
• The value Search for key Polaris.ActionList.SearchField.search is very short. Short strings are more likely to be misunderstood by translators without context. Please provide additional context for the translators if possible.
• The value Search actions for key Polaris.ActionList.SearchField.placeholder is very short. Short strings are more likely to be misunderstood by translators without context. Please provide additional context for the translators if possible.

Please look out for other instances of this issue in your PR and fix them as well if possible.

Questions about these messages? Hop in the #help-localization Slack channel.

[lgriffee]

LGTM! 🎉🚢✨💯

[lgriffee]

Suggested change

	Update `Checkbox` styling to improve mobile consistency
	Updated `Checkbox` styling to improve mobile consistency

[aveline]

By replacing this icon we are removing the checkbox icon animation that was added for the new design language, just wanted to confirm this is intentional @heyjoethomas?