input: specify mode when capturing pointer in tests

Since we're about to add another capturing mode in addition to ABSOLUTE,
make the PointerCaptureRequest constructor take the mode as a parameter,
and explicitly state it when capturing in tests.

Bug: 403531245
Test: $ atest --host inputflinger_tests
Flag: TEST_ONLY
Change-Id: I1d8a8085c7e12812c206b98d8f6e01a303a8381c