input: specify a mode when capturing the pointer

Currently there are only two modes, UNCAPTURED and ABSOLUTE, which are
equivalent to the existing uncaptured and captured states respectively,
but this will allow us to add a new RELATIVE mode in upcoming changes.

Test: check that a test app can still request and release capture, and
      receives events as appropriate in each state
Test: $ atest --host inputflinger_tests
Test: $ atest CtsInputTestCases:android.input.cts.\
              {TouchpadAbsoluteCaptureModeTest,MouseCaptureTest}
Bug: 403531245
Flag: com.android.hardware.input.pointer_capture_modes
Change-Id: Ibb9d382ec76a109a91898194c3557d60a19b2bdb