Remove a dependency on IMMS#getCurMethodLocked()

With this CL

  InputMethodManagerService#onUpdateEditorToolTypeLocked()

stops relying on

  InputMethodManagerService#getCurMethodLocked(),

which should be removed in favor of concurrent multi-user support.

There must be no observable behavior change in single-user mode, and
stylus handwriting is not yet supported in multi-user mode anyway.

Bug: 350386877
Test: presubmit
Flag: EXEMPT refactor
Change-Id: Ibc3402146f028abef3937c0e2de3f469ff683c14