Add "Show advance settings" support to the file download rows

[arraypress]

trafficstars

Enhancement Request

Explain your enhancement (please be detailed)

I need to add an additional data for each downloadable file, so files can be "previewed" before being downloaded (in this case assigning preview mp3s, images, etc). While programatically adding another "row" under the file can be done, it looks ridiculous (and confusing) to the user. So my solution was this:

Ideally, I would like the ability for the file form rows to support "Show advanced options" like the variable price rows. This would allow me to hide these fields on load and make things neater and more accessible (for people who need them).

Justification or use case

EDD add-on plugin development.

[arraypress]

Submitted PR for this one: #9583