ViewRootImpl: call requestPointerCapture through InputManager

We're trying to get rid of InputManagerGlobal#getInstance.

Bug: 403531245
Test: check that a test app can still request and release capture, and
      receives events as appropriate in each state
Test: $ atest CtsInputTestCases:android.input.cts.\
              {TouchpadAbsoluteCaptureModeTest,MouseCaptureTest}
Flag: EXEMPT refactor
Change-Id: If3e2b6da5103ed80dc7f5d4d506d951af5806a98