Retrieve the caller's selected method id in start input

For beter user consistency in startInput, this CL also paramaterize
computeCurrentDeviceMethodIdLocked by passing the user id.

This CL represents an internal refactoring and shouldn't introduce any
observable breakage.

Bug: 325515685
Bug: 341558132
Test: atest CtsInputMethodTestCases
Test: atest FrameworksServicesTests
Test: atest --host FrameworksInputMethodSystemServerTestsRavenwood
Test: presubmit

Change-Id: I910ae5641f14464881da6c3916fb6f5d6418c709