InputDispatcher: dump window in a separate function

This makes it more convenient to dump windows from other places during
debugging. For example, this could also be called from setInputWindows
to inspect all of the window flags that might be changing.

Bug: 312714754
Test: adb shell dumpsys input
Change-Id: I2ace23bec1231f3a318e1b6a19f146b588e077b6