Add manage mode workflow for ExternalStorageProvider

In Scoped Storage world, access to "Android/data" style directories are
hidden for privacy reasons. Allow ExternalStorageProvider to show these
hidden files when in manage mode.

Bug: 150366834
Test: Android/data and Android/obb is visible from Files App, but are
hidden in Picker view from StorageTestApp and Gmail (GMAIL > Compose >
Attach > Go to Pixel > Android)

Change-Id: I58b4fc23d9b479df4fc0480ae55f1f2070d0cb7c