The behavior of `window.cursor_position()` is not same cross platforms when enable cursor hittest

## Bevy version

0.10

## \[Optional\] Relevant system information

OS: Win10 & MacOS

## What you did

When enable cursor hittest in `window_fallthrough` example,
- On Win10, `window.cursor_position()` will always return `None`
- On MacOS, `window.cursor_position()` will return `Some` if inside window, or `None` if outside window

## What went wrong

The behavior is not same cross platforms.