Add SYNCHRONOUS to EnabledFlags for PackageManager

SYNCHRONOUS is a flag for setComponentEnabledSetting()
which will serialise the given user's package restrictions
state (including enabled + disabled packages) after the
specified component state has been updated.

Test: manual
Bug: 130044763
Change-Id: I615e5af6361718b5f3c355ca4424d1f8c4fb078f
Signed-off-by: Julius D'souza <jdsouza@google.com>