feat: introduce BrowserType.name()

[aslushnikov]

This helps a lot to produce nice logging:

const { chromium, webkit } = require('playwright');

(async () => {
  for (const launcher of [chromium, webkit]) {
    console.log(`Testing on ${launcher.name()}`);
    const browser = await launcher.launch();
    // ...
    await browser.close();
  }
})();