onBidWon sometimes runs on s2s bids

[dgirardi]

Type of issue

Bug / Improvement

Description

An adapter's onBidWon handler will run on s2s bids if it's included in the bundle, but obviously not if it isn't. Besides the difference in behavior in itself, it's likely that not all adapters can actually accept an s2s bid in their onBidWon handler: they may expect it to be one that they generated. For example:

Prebid.js/modules/adpartnerBidAdapter.js

Lines 124 to 138 in ec182d0

	onBidWon: function(data) {
	data.winNotification.forEach(function(unitWon) {
	let adPartnerBidWonUrl = buildUrl({
	protocol: ENDPOINT_PROTOCOL,
	hostname: ENDPOINT_DOMAIN,
	pathname: unitWon.path
	});
	if (unitWon.method === 'POST') {
	spec.postRequest(adPartnerBidWonUrl, JSON.stringify(unitWon.data));
	}
	});
	return true;
	},

Proposal

The new onBidBillable method to be introduced for #4494 will be invoked only for client side bids.
Starting from version 8, onBidWon will also be invoked only for client-side bids.

[patmmccann]

#8539