Use ActivityStarter instead of context to start activities in SysUI

- The ActivityStarter will handle launching the dialog to the actual foreground user

Bug: 323072039
Flag: EXEMPT bugfix
Test: Manual testing
atest -c SystemUiRoboTests:InternetAdapterTest \
         SystemUiRoboTestsInplace:InternetAdapterTest
atest -c SystemUITests:InternetDialogDelegateControllerTest

Change-Id: I0cfd225b243555b333a6658f9501c356e9313c7c