Move hidden ApplicationInfo flags into a separate field.

The public API field android.content.pm.ApplicationInfo.flags can
support only 32 flags. This limit has been reached. As a short term
workaround to enable new public flags to be added, this CL moves flags
which are not public API into a separate new field privateFlags and
renames the affected flags constants accordingly (e.g., FLAG_PRIVILEGED
is now PRIVATE_FLAG_PRIVILEGED).

The new privateFlags field is not public API and should not be used
for flags that are public API.

The flags that are moved out of ApplicationInfo.flags are:
* FLAG_HIDDEN,
* FLAG_CANT_SAVE_STATE,
* FLAG_FORWARD_LOCK, and
* FLAG_PRIVILEGED.

NOTE: This changes the format of packages.xml. Prior to this CL flags
were stored in the "flags" attribute. With this CL, the public flags
are stored in a new "publicFlags" attribute and private flags are
stored in a new "privateFlags" attribute. The old "flags" attribute
is interpreted by using the old values of hidden/private flags.

Change-Id: Ie23eb8ddd5129de3c6e008c5261b639e22182ee5