Add required flag to receivers in LatinIME

Android T allows apps to declare a runtime receiver as not exported
by invoking registerReceiver with a new RECEIVER_NOT_EXPORTED flag;
receivers registered with this flag will only receive broadcasts from
the platform and the app itself. However to ensure developers can
properly protect their receivers, all apps targeting U
and registering a receiver for non-system broadcasts must
specify either the exported or not exported flag when invoking
registerReceiver; if one of these flags is not provided, the
platform will throw a SecurityException. This commit updates
the dictionary receivers with the RECEIVER_NOT_EXPORTED flag since
these are only sent from the local app. The HIDE_SOFT_INPUT
receiver is flagged with the RECEIVER_EXPORTED flag since it
can be sent by any app with the corresponding permission.

Bug: 234659204
Test: Build
Change-Id: I2b9a1360e0eb1c1965c07cc71dca9f11eb153517