Spec "Referer" and "Origin" headers in reporting beacons.

[blu25]

This PR specs the following behavior:

• Setting the "Origin" header to the origin of the frame that invoked reportEvent() for destination URL events.
• Setting the "Origin" header to the worklet's origin (which we are calling reporting url declarer origin) for destination enum and automatic beacon events.
• Setting the "Referer" header to the ad frame root's origin (which we are calling initiator ancestor root origin) for automatic beacons triggered by component ad frames.
• Setting the "Referer" header to the origin of the frame that triggered the beacon for all beacons triggered not by component ads.

See this document for notes/reasonings on why things were done the way they were.

There will need to be a separate effort in the Protected Audience spec to set some of the values that these changes are expecting to be set. More specifically:

• The new reporting url declarer origin variable will need to be set during the asynchronously finish reporting when it invokes finalize a reporting destination.

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