DO NOT MERGE: De-guava BroadcastInterceptingContext and move it to testutils.

Removing the static dependency on guava reduces test compile time
by about 20 seconds on a Z840, thus substantially speeding up the
compile/test cycle.

Make FutureIntent public instead of package-private because it is
used directly by NetworkPolicyManagementServiceTest, which as of
this CL is now in a different package.

(cherry picked from commit 281a17c9)

Test: runtest frameworks-services -c com.android.server.ConnectivityServiceTest  # PASS
Test: runtest frameworks-services -c com.android.server.NetworkPolicyManagerServiceTest  # PASS
Test: runtest frameworks-services -c com.android.server.net.NetworkStatsServiceTest  # PASS
Test: runtest frameworks-services -c com.android.server.NetworkManagementServiceTest  # Already failing.
Bug: 31479480
Change-Id: Ifab32c9214e9caab71dbf93b3d3ca88df6f49636