DolphinNoGUI: Receive resize events and notify backend when this occurs

[stenzek]

Solves the viewport sizing issue for backends that cannot tell when the window is resized (Vulkan on NV at least).

Should fix this issue: https://bugs.dolphin-emu.org/issues/9894

There's some duplication in the event handler here, we could probably XGetGeometry call by using the event instead, might do this if it fixes the issue linked.

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This change is 

[degasus]

LGTM

Do you think it's worth to implement this kind of logic also with WX?
https://github.com/dolphin-emu/dolphin/blob/master/Source/Core/VideoBackends/OGL/Render.cpp#L1777

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Reviewed 1 of 1 files at r1.
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Comments from Reviewable

[stenzek]

I think it'd be a good idea, and it's something I've been wanting to do for a while now (at least getting rid of the polling each frame).

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Review status: all files reviewed at latest revision, all discussions resolved, all commit checks successful.

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Comments from Reviewable