fix two issues related to hb_uuid and hb_cache_id targeting keys

[jsnellbaker]

Type of change

• Bugfix

Description of change

This PR incorporates some fixes related to the hb_uuid and hb_cache_id targeting keys.

Some issues that were fixed:

• due to the order in which the code was executed, the bid.adserverTargeting.hb_uuid and bid.adserverTargeting.hb_cache_id fields weren't properly populated with the bid's videoCacheKey after it came back from Prebid Cache. This caused other functions that pulled the targeting keys (like pbjs.getAdserverTargetingForAdUnitCode()) to be missing this information when it was otherwise expected to be there.

• a consequence to the above issue, when the publisher tried to overwrite the values for these keys in the pbjs.bidderSettings feature - the overwrites wouldn't work because the bid.videoCacheKey wasn't populated at the time these bidderSettings values were used.

The changes in this PR addresses the above issues through mainly moving the code around to populate the bid.adserverTargeting object once we know the bid is complete (ie back from prebid cache for that use-case).

Note - removed the dfpAdServerVideo code since it's now redundant.

[mkendall07]

LGTM