DO NOT MERGE Apply a maximum char count to the load label api

The system is overwhelmed by an enormous label string returned by
the load label api. This cl truncates the label string if it exceeds
the maximum safe length.

Also update the max safe label length to 1000 characters, which is
enough.

Bug: 67013844
Test: atest PackageManagerTest
Change-Id: Ia4d768cc93a47cfb8b6f7c4b6dc73abd801809bd
Merged-in: Ia4d768cc93a47cfb8b6f7c4b6dc73abd801809bd
(cherry picked from commit b55d314f)