Add flash to AR Camera

[jtklein]

This issue was originally added to the https://github.com/inaturalist/react-native-inat-camera:

On the AR camera, we want to add an option to turn on the camera flash while the user is using the camera. I have two options, with option 1 being the preferred route.

1. My ideal scenario is to have a button that can be clicked on and off, so that the flash can remain on while the user is using the AR Camera to scan, and not just when they take a photo. That would make the Camera easier to use in low light, and would also make it easier to focus on organisms with the flash constantly on. This would mean there are two states that the user can toggle by pressing the flash button, which would turn the camera flashlight on and off:

• flash OFF (default state): flashlight is off while the AR camera is open
• flash ON: flashlight is on while the AR camera is open

2. If that's not feasible, the flash could function similarly to how most camera phones do flash: only going off when the shutter button is pressed to take a picture. This would mean three states that the user can toggle between. These states can be changed at any time, and only affect the behavior of the flash after the camera button is pressed:

• flash AUTO (default state): when shutter button is pressed, flash will go off depending on how light/dark it is
• flash ON: when shutter button is pressed, flash will go off
• flash OFF: when shutter button is pressed, flash will not go off

I've added states for all of these on Zeplin:

• flash ON
• flash OFF
• flash AUTO

I will create custom flash icons for these, so when folks begin working on this, let me know and I'll get those icons over to you.