Decouple direct dependency on MainContentCaptureSession

MainContentCaptureSession is the implementation class. The dependency
should only use its base class.

Test: CtsContentCaptureServiceTestCases, MainContentCaptureSessionTest.
BUG: 309411951
Change-Id: I5f8c4795622c5c826f103f19fbb82922b539594e
10 files changed