[Gtk] Partial workaround for embedding an NSView inside a ScrolledWindow
[Gtk] Partial workaround for embedding an NSView inside a ScrolledWindow

Manually reposition the NSView when the enclosing viewport is scrolled.
Unfortunately, the NSView is still not clipped properly.

This is only meant to be a stopgap until the gtk stack is fixed,
at which point this commit should be reverted.

sevoku/xwt,iainx/xwt,antmicro/xwt,directhex/xwt,hwthomas/xwt,residuum/xwt,lytico/xwt,hamekoz/xwt,cra0zy/xwt,mono/xwt,mminns/xwt,steffenWi/xwt,akrisiun/xwt,TheBrainTech/xwt,mminns/xwt