Update ImGui window positions on every resize

[ZeroInternalReflection]

Summary

None

Purpose of change

When the Cataclysm window is resized, the position of any ImGui windows is not correctly updated, so windows that are supposed to be centered end up misaligned
Fixes #72058

Describe the solution

Set cataimgui::window to update the position each time it's resized. The previous setting "ImGuiCond_Appearing", apparently only actually moves the window when it's first created/unhidden.

Describe alternatives you've considered

Testing

Existing UI behaviour:

Old_UI_Behaviour.mp4

Current ImGui behaviour:

Current_ImGui_Behaviour.mp4

After this change:

ImGui_Correct_Repositioning.mp4

Additional context

[mqrause]

That seems to only be an issue if you use -1 for x and y in get_bounds? At least it properly repositions in #55503.

Edit: I should read the actual code first. Yeah, this is explicitly for the -1 case because that tries to center the window.