[CODE] vgui_controls library doesn't compile when included outside of client.dll

[Blixibon]

Describe the bug

vgui_controls.lib fails to compile when using a custom project which integrates it because it looks for g_bUsingCustomHudAnimations, a value extern'd from the client DLL.

Steps to reproduce

Steps to reproduce the behavior:

1. Use vgui_controls.lib in a non-client.dll project
2. Attempt to compile
3. error LNK2001: unresolved external symbol "bool g_bUsingCustomHudAnimations"

Expected behavior

vgui_controls.lib integration should be supported on any project, not just the client DLL.

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Additional context

This has manifested with users trying to integrate the new Gamepad UI project into Mapbase mods, although other, older projects integrate vgui_controls.lib outside of the client as well.

This can easily be fixed by just moving g_bUsingCustomHudAnimations to vgui_controls and making the client look for it instead.