Split ContentCaptureSession in 2 classes.

This is just a refactoring for now, but it paves the way to support children
sessions.

Bug: 121042846
Bug: 117944706

Test: atest CtsContentCaptureServiceTestCases

Change-Id: I64bb5562dcfd4a9f0f69bb13009e4cf47a4f3b37
5 files changed