TouchpadInputFuzzer: always set X and Y axes

The GestureConverter constructor assumes that these are always present
(since a device shouldn't be classified as a touchpad, and so the
GestureConverter shouldn't be created, if they aren't) so the fuzzer
should always have them present.

Test: $ SANITIZE_TARGET=hwaddress \
        make inputflinger_touchpad_input_fuzzer
      (See b/383345057#comment13)
Bug: 383345057
Flag: TEST_ONLY
Change-Id: I321efb42e24ee4e0ce9bf75806cffa19a72c8b0b