differentiate aconfig flags and legacy flags in device config dump

Now with the aconfig text proto files dumped to different device
partitions during build time, we can use these textproto files as source
of truth to tell which flags are aconfig flags among device config
flags. This allows us to update device config bugreport dump to create a
section dedicated for aconfig flags

Bug: b/291770670
Change-Id: I6d3422ba4d8dd7db33db12e4b6b1b824e1631e0a