Add @TestApi to set mouse scaling for any display

Currently disabling mouse scaling is only possible for VirtualDisplay.
As connected displays tests are being developed, testing VirtualMouse
interaction in / between default display and overlay/virtual displays
are required for better coverage.

Bug: 405848641
Test: atest CtsInputTestCases
Flag: EXEMPT test_only
Change-Id: I11b486d9a86b810e7e20a6e0cb46f8e97b55efeb