feat(ajax): add params query string parameter configuration

[benlesh]

Adds a feature that will accept a wide variety of possible inputs for params to set the query string parameters for ajax.

Note that this feature will require a polyfill for URLSearchParams in IE, but this is not a breaking change for IE, as if they do not use this feature URLSearchParams is never accessed. Adds documentation and relatively thorough tests.

Related to #5384

[benlesh]

Everything inside of this conditional is the bulk of what was added. Please notice that it's mostly comments, and not actually a lot of code. Also worth noticing that URLSearchParams is only ever accessed inside of this conditional.

[cartant]

LGTM. Just a nitpick and what looks like a copy/paste error in a test. Approving this 'cause the latter needs no discussion.

[jayphelps]

Late to the party here, but note that “params” can also mean (and IMO more often refers to) route params a la Express ‘/products/:productId’ Express’s API calls these ‘params’. Angular and many others do as well.

I suggest naming it query, queryParams, search, or searchParams, to follow naming conventions used elsewhere. My gut says queryParams is probably the right choice since that’s what Angular uses: https://angular.io/api/router/NavigationExtras

[cartant]

@benlesh +1 from me for queryParams ☝

[benlesh]

I'm out this morning, but if someone puts a PR in to change it, I'm down.