Use BUILD_*_IMAGE flags in add_img_to_target_files.

Modify add_img_to_target_files.py to use the BUILDING_*_IMAGE flags when
deciding whether to create and add a given image to a target files
archive.

To do this, the BUILDING_*_IMAGE flags are now dumped to misc_info.txt.

The origin of this change was to use the BUILDING_USERDATA_IMAGE and
BUILDING_CACHE_IMAGE flags in add_img_to_target_files.py so that we
could reliably turn off the generation of the userdata and cache images.
The other image flags were added for symmetry.

Bug: 130307439
Test: m -j out/target/product/bonito/misc_info.txt
Test: m -j droid dist
Change-Id: I32d5a8d6c9ebb5f329d856030084d698ee8d271d