floss: Complete libflags shim

On Floss we store the aflags config inside sysprops module.

Bug: 307006275
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: atest --host bluetooth_test_gd_unit:ConfigCacheTest#test_get_section_property_names
Test: atest --host bluetooth_test_gd_unit:SyspropsModuleTest
Test: manual set/reset/remove persist.device_config.aconfig_flags.bluetooth.com.android.bluetooth.flags.msft_addr_tracking_quirk,
      verified behavior changed
Flag: EXEMPT, Floss-only changes
Change-Id: I1d72b7e970d354a6b8c22e6e015d859bd1b48da7