Dynamically determine ajaxPageState based on libraries

After 📌 Compress aggregate URL query strings Fixed the list of libraries (in both 'include' and 'exclude') in the query strings is compressed.

However, for 📌 Allow AJAX to use GET requests Fixed , we probably want ajax_page_state itself to be compressed too so it's not too long as a query parameter (currently sent in POST to AJAX requests). I haven't actually implemented this bit yet, but it's probably the next step for that issue - at least a proof of concept to see how tricky it is.

Since we don't actually use the library information in ajax_page_state in JavaScript, just pass it around, I think the fact it's compressed probably won't matter at all for this issue.

#3348789-21: Compress ajax_page_state → might make this harder, since it compresses all of ajaxPageState not just the libraries, but we should probably just try and see.

Another thing I didn't think of before, but affects this, is that we only put the libraries in the query string when aggregation is on, but we still need ajaxPageState when aggregation is off, so would have to do something when there's all the individual CSS and JS added to the page too.