Capture the contents of a single task

Introduces layer mirorring of a single task, given the task is both
identified (future work - dependency on setup flow in SysUI) and the
flag is enabled (currently disabled).

Error handling (tearing down the VirtualDisplay if task recording setup failed)
will come in a future change

Bug: 216625226
Test: atest WmTests:DisplayContentTests
Test: atest WmTests:ContentRecorderTests
Change-Id: I16abd55ce75537ff8fbbb379e4970668ea02a230