Move static functions to InputConsumer cpp file

This way, they can be reused by other code in that file. For example,
by the new "InputConsumerNoResampling".

Also, pass the parameters by ref because they are not nullable.

Bug: 311142655
Test: m libinput libinput_tests
Change-Id: Ib40bcddfcb3d49b0a42d58533dcc566d9d49a500