Jetpack Comments: nested comments with async load of comments

#### Is your feature request related to a problem? Please describe.

When comments are loaded asynchronously in a template, the Jetpack Comments module won't work for nested comments.

Jetpack Comments is enqueuing the `watch_comment_parent()` function/script in `comment_form_before()` function using the `wp_footer` action hook. Loading the comments asynchronously, the `wp_footer` hook is already executed and no event listeners would be added. This is preventing the nested comments to work as the `comment_parent` hidden field won’t be updated.

#### Describe the solution you'd like
I would like the JS in the `watch_comment_parent()` function to be accessible outside of the closure with any kind of hook/API that we could trigger for this async use case

#### Describe alternatives you've considered
A workaround would be for the async comments to include this js snippet as well when the comments are loaded which is working but it sums up in mostly in copy-pasting the JS from `watch_comment_parent()` which is not elegant neither will be future proof if the Jetpack Comments feature evolves.

#### Additional context
n/a

Start by reading the Jetpack Comments implementation around watch_comment_parent(), comment_form_before(), and the wp_footer action. Trace how asynchronously loaded comments reach the comment form, then determine an accessible hook or API that can re-enable nested-comment behavior without copied JavaScript. Done means nested comments work after async loading and the existing behavior remains intact.

Written by the indexing model from the issue text.