Allow the use of input features for windowless windows

In particular spy windows are specified in input features. Windowless
windows are more lightweight than regular windows in implementing spy
windows.

It also helps overlays (e.g. window decorations) to pass input events to
app content, and only consume them when necessary.

Bug: 266866903
Test: Input of window decorations still work.
Test: atest WmTests:WindowManagerServiceTests
Change-Id: Ifbd2bc1a5966325b5bc28e58a19fcd3e05aafdf2