Use URLSearchParams after we drop IE support

[samreid]

https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams looks great but is not supported on IE. Once we drop IE support, this could clean up our parsing logic.

[zepumph]

We have dropped support for IE. I'm going to assign myself and @samreid, feel free to unassign if you aren't interested at this time.

[samreid]

I'm glad we can do this now, but it would not be a priority for me for several months. I support you!