url: extend URLSearchParams constructor (whatwg #175)

[jasnell]

Refs: whatwg/url#175

Proposes the ability to construct URLSearchParam instances using object and Iterable in addition to string. It is not yet clear if this will be added to the spec, but if it is, we will need to update the implementation.

[TimothyGu]

CC: @nodejs/url

[jasnell]

This landed in the spec... now needs to be implemented.
Refs: whatwg/url#175 (comment)

[TimothyGu]

I'd like to merge #10399 first, which will simplify the process of implementing this.

[TimothyGu]

Also needed to be tracked is whatwg/url#204.