Support repeated names

[Janpot]

https://url.spec.whatwg.org/commit-snapshots/31ddc5bd0c4ca1b6d837029c926ec87bc472c168/#example-constructing-urlsearchparams

Otherwise, if init is a record, then for each mapping (name, value) in init, append a new name-value pair whose name is name and value is value, to query’s list.

I propose to also add support for multiple values

new URLSearchParams({ x: ['1', '2'], y: 3 });
// x=1&x=2&y=3

Basically: when value is an array, for each item in that array, add a new name-value pair whose name is name and value is that item

[TimothyGu]

Duplicate of #204

[Janpot]

Missed that, thanks!