Generates an Fxfs image containing a blob volume with the blobs specified in manifest_path.
Creates the block image at output_image_path and writes a blobs.json file to
json_output_path.
If target_size bytes is set, the raw image will be set to exactly this size (and an error is
returned if the contents exceed that size). If unset (or 0), the image will be truncated to
twice the size of its contents, which is a heuristic that gives us roughly enough space for
normal usage of the image.
If sparse_output_image_path is set, an image will also be emitted in the Android sparse
format, which is suitable for flashing via fastboot. The sparse image’s logical size and
contents are identical to the raw image, but its actual size will likely be smaller.