[Box] Update border radius props to match web spec

[kyledurand]

WHY are these changes introduced?

Fixes #10064

Playground

import React from 'react';

import {Box, Page, VerticalStack} from '../src';

export function Playground() {
  return (
    <Page title="Playground">
      {/* Add the code you want to test in here */}
      <VerticalStack gap="3">
        <Box padding="3" background="bg-caution" borderRadius="3">
          control{' '}
        </Box>
        <Box padding="3" background="bg-caution" borderStartStartRadius="3">
          border start start radius
        </Box>

        <Box padding="3" background="bg-caution" borderStartEndRadius="3">
          border start end radius
        </Box>

        <Box padding="3" background="bg-caution" borderEndStartRadius="3">
          border end start radius
        </Box>

        <Box padding="3" background="bg-caution" borderEndEndRadius="3">
          border end end radius
        </Box>
      </VerticalStack>
    </Page>
  );
}