Add ImGuiWindowFlags_NoPosClamp

[TheMode]

Add a flag to prevent window position clamping, useful if you wish to have windows off-screen.

Doesn't currently work on docked windows

Solve #8483

[TheMode]

Perhaps that a way to differentiate manually moving a window out of bounds (which should probably still clamp) and programmatically through SetWindowPos would work better.

Or perhaps again, an alternative to GetMainViewport specifying workspace bound (defaulting to main viewport)