Complete event model migration for pageNavigation, linkExposure, socialMediaLinkSharing, and idle

[jonathanmayer]

In the early versions WebScience, we implemented a measurement and storage model for these modules (i.e., each module ran an individual measurement and stored records of that measurement). We have partially transitioned to a WebExtensions-like event model for these modules, and there are some remaining items to complete.

Remaining items for pageNavigation:

• Implement support for adding and removing multiple pageDataCallback listeners with differing PageDataOptions values.
• Add logic to ensure that the associated content script only runs once per page.

Remaining items for linkExposure:

• Implement support for adding and removing multiple linkExposureCallback listeners with differing LinkExposureOptions values.
• Integrate untracked link exposures into linkExposureCallback and LinkExposureDetails, rather than using different (and undocumented) callback and detail types for untracked exposures. Note that the meaning of an untracked link will vary by listener, depending on its match patterns.
• Add logic to ensure that the associated content script only runs once per page.

Remaining items for socialMediaLinkSharing:

• Implement support for adding and removing multiple socialMediaShareCallback listeners with differing SocialMediaShareOptions values.
• Correct the documentation for SocialMediaShareOptions.
• Add documentation for SocialMediaShareDetails.

Remaining items for idle:

• Implement support for removing onStateChanged listeners.

[jonathanmayer]

A stale list of items for socialMediaLinkSharing: citp/news-disinformation-study#64