Verify that EditorInfo.packageName and uid are consistent

Currently EditorInfo.packageName is filled in the application
process and passed to the IME without any verification.

With this CL, the system makes sure that the provided package
name and application's uid are consistent before establishing
the input connection.  In other words, the risk of spoofed
EditorInfo.packageName will be mitigated with this change.

This should be beneficial especially when an IME wants to have
per-application settings and/or dictionaries.

Bug: 18931038

Change-Id: Ib871141e3381e45c2623c5f4d692da7a7e78fcc5