Add back "setFastPairScanEnabled" RPC method for e2e tests.

This change add back "setFastPairScanEnabled" RPC method in the
test snippet which is required to the test scripts. Due to the
@hide notation , ProGuard shrink out the
NearbyManager.setFastPairScanEnabled method, we directly use
Settings.Secure.putInt to manipulate FastPairScan setting as
a workaround.

Bug: 227513829
Bug: 228406038
Test: atest -v CtsNearbyMultiDevicesTestSuite
Reason for revert: Makes e2e tests working and pass
Partial Reverted Changes:
I4bdf8653d:Remove fast pair scan API
Ignore-AOSP-First: nearby_not_in_aosp_yet
Change-Id: I205f805dad2ca0ba92b8325dcc75bc62f74e76cb

Change-Id: I90e2c294cde7fb65d8fc326e85cd93232a84c4cc
diff --git a/nearby/tests/multidevices/host/Android.bp b/nearby/tests/multidevices/host/Android.bp
index 933cae9..ff795e8 100644
--- a/nearby/tests/multidevices/host/Android.bp
+++ b/nearby/tests/multidevices/host/Android.bp
@@ -17,6 +17,7 @@
 }
 
 // Run the tests: atest -v CtsNearbyMultiDevicesTestSuite
+// Check go/run-nearby-mainline-e2e for more details.
 python_test_host {
     name: "CtsNearbyMultiDevicesTestSuite",
     main: "suite_main.py",