support destructuring assignment as separate es feature

[alexander-akait]

For let we have file https://github.com/Fyrd/caniuse/blob/master/features-json/let.json, but for destructuring assignment we don't have it, it is strange because we have https://caniuse.com/mdn-javascript_operators_destructuring page

Ref: webpack/webpack#11876

Why it is a problem? Because IE 11 supports part of es6, for example destructuring assignment is not supported

Maybe we should separate all es6 features

[Fyrd]

The "let" data is part of the caniuse database while the "destructuring assignment" data comes from MDN (see https://github.com/mdn/browser-compat-data/blob/master/javascript/operators/destructuring.json ).

While I won't disallow data that's already part of the MDN BCD to be added to the caniuse database, it's not going to be a priority for me to add since it can already be found on the site.