classes/package: fix FILES_INFO serialisation in pkgdata
The FILES_INFO entry in each pkgdata file stores the list of files for
each package. Make the following improvements to how this is stored:
* Store paths as they would be seen on the target rather than
erroneously including the full path to PKGDEST (which is specific to
the build host the package was built on)
* For simplicity when loading the data, store complete paths for each
entry instead of trying to break off the first part and use it as the
dict key
* Record sizes for each file (as needed by Toaster)
* Serialise the value explicitly using json rather than just passing it
through str().
Fixes [YOCTO #5443].
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
