Use _activityPubOptions at runtime

[mattwiebe]

It turns out that #1131 breaks stuff on dotcom. But even printing in wp_head wasn't good enough, because the scripts were demanding the option to be present at instantiation time. But with a more flexible approach, we can assume that the option will be there at runtime, which is good enough. So I introduced a getOptions helper to do that.

Note that we could get around this by adding proper inline script dependencies to each script in turn, but that was giving problems with the script handles registered through block.json via register_block_type_from_metadata. This is why I moved to just outputting it.

Testing

All blocks, in editor and the frontend, should keep working properly