[Feature request] Start with flash on for document scanner

**What's your feature request? Please describe.**
For my app people are usually doing document scanning in dim conditions, hence I'd like to have the flash turned on by default to avoid having them click the icon each time.

**Mobile environment**
Android

**Additional context**
As stated above, having an option to start with flash turned on would spare a lot of clicking.
I also tried turning on flash before starting document scanner, but it would turn it off upon start.

Start by locating the Android document scanner entry point and the code that initializes flash behavior. Check how the existing flash toggle is applied when scanning starts. Done means the scanner can start with flash enabled by default without breaking the manual flash control.

Written by the indexing model from the issue text.