Add examples for BigInt API

[Elchi3]

Examples for:

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt/asIntN
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt/asUintN
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt/toLocaleString (only works in Chrome 76 for now, soon in Nightly)
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt/toString
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt/valueOf

[wbamberg]

Thanks @Elchi3 and sorry to take so long reviewing.

[Elchi3]

Thanks for the review, @wbamberg. Sorry to have poked about this one, but I thought it would be great to land it this week since we're shipping and advertising it. Addressed your comments. Great feedback as always!

[wbamberg]

Thanks @Elchi3 , looks great. I also noticed that the "expected output" included quotes for the bigint values in asIntN() and asUintN(), which it should not.

Since it's a trivial change to remove the quotes I just made it so as to avoid another review round.

[Elchi3]

Thanks for the quick fix! ❤️