Allow Cursor option for the filepicker

[radar07]

Is your feature request related to a problem? Please describe.
It's nice to allow the user to set the cursor for the file picker. (Default is >).

Describe the solution you'd like
When the user sets the custom cursor option like the one below,

the output could be something like the below

Additional context
I'm unsure if this is a feature or a bug because the gum file-picker allows the option to set the cursor but it isn't working. Please see this issue

[radar07]

I'd love to raise a PR. Thanks:)