Fix Autosuggest bugs

[JakePT]

Description of the Change

Fixes two Autosuggest issues.

1. An issue where older Autosuggest filter functions were not automatically applies as hooks for backwards compatibility. This can happen if the filter function was defined after the backwards compatibility code is run. This fix defers the backwards compatibility code to run on the load event.
2. An issue that prevented clicking Autosuggest suggestions if they had been customized with additional markup. The Autosuggest click listener did not work properly if elements were added inside the .autosuggest-link element, so this fix updates the event listener to work no matter how many child elements exist.

Closes #3095
Closes #3107

How to test the Change

• Adding filters to Autosuggest using the <=4.3.0 method should work even if the filters are defined in a script that runs after ElasticPress' autosuggest.js.
• Clicking Autosuggest suggestions should work as expected when filtering the item HTML with this HTML, and it should continue to work with the default HTML.

Changelog Entry

Fixed - An issue that caused Autosuggest filter functions to no longer work.
Fixed - An issue that prevented clicking Autosuggest suggestions if they had been customized with additional markup.

Credits

Props @JakePT

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.