[Select] change text-rendering to auto to fix Safari bug

[dleroux]

WHY are these changes introduced?

Fixes https://github.com/Shopify/web/issues/18619

As outlined here webkit has a bug that cause the browser to crash when a select text-rendering is set to optimizeLegibility

WHAT is this pull request doing?

Changes the text-rendering of the Select input to auto

How to 🎩

In the playground, navigate to the Select examples and ensure that on Safari 13 the browser doesn't crash.

Copy-paste this code in playground/Playground.tsx:

import React from 'react';
import {Page} from '../src';

export function Playground() {
  return (
    <Page title="Playground">
      {/* Add the code you want to test in here */}
    </Page>
  );
}

🎩 checklist

• Tested on mobile
• Tested on multiple browsers
• Tested for accessibility
• Updated the component's README.md with documentation changes
• Tophatted documentation changes in the style guide
• For visual design changes, pinged one of @ HYPD, @ mirualves, @ sarahill, or @ ry5n to update the Polaris UI kit

[danrosenthal]

🎩