NSOpenGLContextView couples the window manager logic tightly with
OpenGL. Use generic NSViews, and attach NSOpenGLContext just like the
other platforms.
This change prepares for supporting GPU contexts created by clients as
well as a future Metal port.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Package wm (for "window manager") is a better fit for the package, and
distinguishes it from the low-level package windows for the Windows API.
Signed-off-by: Elias Naur <mail@eliasnaur.com>