Allow Media Library "Load More" count to be customizable

[antpb]

In #53827 it was reported that the count of items loaded when clicking the "load more items" button in the Media Library was too low and caused many clicks to get to an item that folks wanted.

In 53827 we are increasing the count from 40 to 80 as a temporary way to solve this issue in a minor release. This value should be configurable in some way.

A future enhancement for this has a few directions we could go
1) Screen Option (which inherits a filter to set a value)
2) Just a plain filter that allows the value to be customized
3) ??? Any better ones?

[pbiron]

My preference would be to add a screen option. this would be analogous to the Number of items per page screen option in list mode.

There has been some talk of "load as many items as are already showing" when the "Load more" button is clicked. That would be kind of hard to do with a screen option, but I'm not sure doing that is a good itea, anyway :-)

[hellofromTonya]

Whoopsie #53787 was already opened to explore how to do this. Closing this one as a duplicate to move the conversation to that ticket.