Update MediaRouter2Manager api

- This CL use the index to get system session instead of use
  getClientPackageName().
- Use getSelectedRoutes() to identify which MediaDevice is
  active device instead of use getClientPackageName().

Bug: 142912244
Test: make -j42 RunSettingsLibRoboTests
Change-Id: I2302cb6bf992a4d679b1753dad3a5bd86b6a8159
2 files changed