Move over our integration with Private Aggregation into our spec. (WI…

…CG#1312)

* Much of the function-level impl, though not fully wired still.

* Some of the reporting args, commit function.

* Rest of collecting stuff into context; pushing it into global contrib
cache is remaining.

* Almost there, still needs to invoke the function and deal with some
refs.

* Fix most imports. Now just need to run the actual report algorithm.

* Maybe fix a build error.

* IDL fix.

* Fix a couple of TODOs, only the big one left.

* Separate context for top-level and actually hook up commit.

* A couple of bugfixes on proofreading.

* When there is a winner, wait till navigation to send requests.

* Fix arg list structure per feedback

* Add a missing </div>

* Update field comment + some function names.

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Co-authored-by: Maks Orlovich <[email protected]>