[Feature] Support Symbol.asyncDispose method (the using keyword) in addition to close()

[dtinth]

This allows us to write this:

await using context = await browser.newContext()
// Code

which is more concise than:

const context = await browser.newContext()
try {
  // Code
} finally {
  await context.close();
}

[mxschmitt]

There scope for this issue is to:

a) support it on all our objects which have a close() method.
b) Make it possible to use the using keyword inside our test runner.

If I forgot something, let us know!