The `a` and `b` parameters to `lerpDouble` have type `num`. This adds
tests for integer parameter values.

Adds tests for lerpDouble for cases where NaN or infinite values are
passed. These tests simply specify the current behaviour.

This re-lands the key event synthesis implementation for Android (Original PR: #19024, Revert PR: #19956). The only difference is sending the synthesized key events to the root view instead of the current view.

Without sending it to the root view, the system doesn't have any chance of handling keys like the back button. The event will still not be sent to the framework twice, since we turn off event propagation while re-dispatching the event.

* Switched PathCommand apply parameter to non-nullable. Add clip op parameter to ClipCommand.

This reverts commit 77dd1c05.