ui/cocoa: Fix absolute input device grabbing issue on Mojave

ui/cocoa: Fix absolute input device grabbing issue on Mojave

On Mojave, absolute input device, i.e. tablet, had trouble re-grabbing
the cursor in re-entry into the virtual screen area. In some cases,
the `window` property of NSEvent object was nil after cursor exiting from
window, hinting that the `-locationInWindow` method would return value in
screen coordinates. The current implementation used raw locations from
NSEvent without considering whether the value was for the window coordinates
or the macOS screen coordinates, nor the zooming factor for Zoom-to-Fit in
fullscreen mode.

In fullscreen mode, the fullscreen cocoa window might not be the key
window, therefore the location of event in virtual coordinates should
suffice.

This patches fixed boundary check methods for cursor in normal
and fullscreen with/without Zoom-to-Fit in Mojave.

Note: CGRect, -convertRectToScreen: and -convertRectFromScreen: were
used in coordinates conversion for compatibility reason.

Signed-off-by: Chen Zhang <tgfbeta@me.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: FA3FBC4F-5379-4118-B997-58FE05CC58F9@me.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>