Implement the TargetFile and BuildInfo

The TargetFile class parses a target-file and provides functions to read
its contents. And the BuildInfo tries to simulate the device with files
on host. Some work it does includes parsing the build properties,
and extracting the image files for partitions specified in the fstab.

Bug: 131911365
Test: unit tests pass, run simulator with cuttlefish, wear devices and from extracted TF.
Change-Id: Iefe4a96d619d2e4b3d038e31480f11a0f9a70afa