[GUI] Fix ti.GUI.MOVE not working on win32 and cocoa

[archibate]

Related issue = A windows Taichi THREE user reports

[Click here for the format server]

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To reproduce:

import taichi as ti

gui = ti.GUI()
while gui.running:
    for e in gui.get_events():
        print(e.type, e.key)
    gui.show()

You should see no Motion event when your mouse is moving above the window. (Didn't have a win env to reproduce yet, but I let that win user to help me confirmed that this is reproduced)
But this works fine on X11:

EType.Move Motion
EType.Move Motion
EType.Move Motion
EType.Move Motion
EType.Move Motion
...

Please merge this fix soon so that windows and mac users could enjoy orbiting camera around in Taichi THREE 😃

@k-ye Would you mind help me confirm the cocoa part works (by using the reproduce code)? Thank in advance!

[JYLeeLYJ]

Hi , this code already works well on Win after my confirmation.

[k-ye]

Thanks LGTM!