healthd: Add charger.recovery module.

This CL splits out healthd_mode_charger_nops for building
charger.recovery. It doesn't change the functionality of the charger
module under recovery, i.e. a) it still doesn't do much work other than
reporting the battery status periodically; b) it keeps calling
device-specific healthd functions (healthd_board_init and
healthd_board_battery_update) via the statically linked HAL.

Previously `charger -r` was used to indicate starting charger under
recovery mode. This CL makes it a noop since we've changed the caller in
recovery.

Bug: 73660730
Bug: 114042635
Test: Boot into charger mode on walleye. Check that charger UI works.
Test: Boot into recovery mode on walleye. Check that /system/bin/charger
      keeps working.
Test: Run charger_test on walleye.
Change-Id: Id91acfcc77ec315c2382392dc54e36c3e85de2eb