fix(FileUploaderButton): refactor to button to remove a11y violation

[tw15egan]

Closes #12725

Refactors the FileUploaderButton to use a button instead of utilizing the label to handle click/keyboard interactions

Changelog

New

• button is rendered adjacent to the label element in FileUploaderButton

Changed

• Moved most props from the label element to the new button element. All functionality should remain the same.
• Updated tests to utilize the button for onClick tests

Removed

• Removed role="button" wherever it was being set, as it is now rendering a button by default
• Removed the tabIndex as this is handled automatically when using a button

Testing / Reviewing

Ensure all of the following:

• All tests pass (especially a11y checker)
• Component renders as expected
• Existing props work as expected
• Functionality remains the same (onClick, onChange can be passed down)

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[tay1orjones]

Looks good! One question below