Use loop for acceptParams

[blakeembrey]

Using a loop here would improve performance for parsing over splitting into an array and iterating over it, then splitting some more. If we prefer the overall split on ; for readability though, we can still avoid the second split by using indexOf instead. There's also some slices and trim that could be avoided for extra performance but it seemed a little overkill for this function.

Finally, given the code is only used here:

express/lib/response.js

Lines 575 to 584 in a46cfdc

	if (key) {
	this.set('Content-Type', normalizeType(key).value);
	obj[key](req, this, next);
	} else if (obj.default) {
	obj.default(req, this, next)
	} else {
	next(createError(406, {
	types: normalizeTypes(keys).map(function (o) { return o.value })
	}))
	}

. If we avoid exporting these utils to users we can just return value only and avoid the rest of the processing entirely.

closes https://github.com/expressjs/security-triage/issues/24

[UlisesGascon]

So far seems much faster!

Report from https://jsbm.dev/ZbkL2XxwbkIOI

[UlisesGascon]

Should we also backport it to v4?