I dont think there is any widget that lets you choose a folder and read/upload all files within it. (Perhaps its logical that such an option doenst exist as folder can have sub folders and it recursively increases)
There is a file dropper widget that you can try and see if it fits your needs.
The default filemanager widget doesnt seem to have the ability for Multiple files (as it architecture idea is different) but if you are going to do a custom/pluggable widget, finally this widget is nothing but a input type=”file” with multiple attribute added to it. Then the browser automatically lets you choose multiple files.