Address Call Streaming API review comments.

1. Make CallStreamingService and StreamingCall SystemApi and hide
2. Add android.permission.BIND_STREAMING_SERVICE
3. Change StreamingCall#DisplayName to CharSequence
4. Hide StreamingCall constructor
5. Fix CallControl#startCallStreaming doc

Bug: 265304561
Test: build; add cts
API-Coverage-Bug: 268061643
Change-Id: I29771cfbf60553eb8325e40b2cd11c5828a445e4