Draft: Support reading bootreason from /proc/bootconfig for charging mode

This is starting to be required on Android 12 devices where the androidboot.* values are no longer on /proc/cmdline.

As tested on Volla Phone X23 this fixes the case of plugging a powered off device to a computer, however plugging to a power brick instead still results in the previously seen strange behavior of seemingly having lomiri-system-compositor etc launch and conflict with the rendered charging animation through Android container.