Camera: Track provider instances

In some very rare corner cases where the binder death notification
gets delayed and races against the new provider 'onRegistration'
callback, camera service can temporarily hold two camera providers
with the same name. Depending on scheduling, if 'onRegistration'
executes first, it will get rejected as the provider name already
exists. The subsequent binder death notification callback will
remove all camera devices.
To avoid this, track all camera providers with a combination of the
provider name and unique instance id. If we receive a registration
callback with provider name that already exists, defer the
initialization sequence until the previous instance gets released
correctly.

Bug: 164019313
Test: cameraservice_test
--gtest_filter=CameraProviderManagerTest.BinderDeathRegistrationRaceTest,
Camera CTS,
Partner testing

Change-Id: I207a12da1fb09b1c45dae8697049f1fec34627d3