Add interactivity pointer

[hello-ashleyintech]

Summary

Events like block_action, views_* events that are sent with interactivity payloads aka (function, function_data) will no longer contain trigger_id but instead a new field called interactivity_pointer. The motivation is to move away from the legacy term "trigger" as it doesn't actually refer to the 2.0 concept of trigger.

This doesn't affect those same events if they are not sent with interactivity payload data (aka regular 1.0 block actions and views events), so there shouldn't be an impact on existing devs / apps.

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[srajiang]

Yay thanks for tackling this! Left some comments for ya.

[srajiang]

Okay! Some documentation comment suggestions here to wrap up, but the changes to the types are looking good to me.

Let's branch next-gen off main and point this branch to merge to that. That way we'll be all set up for cutting the beta release of web-api.