New vgui support api

[a1batross]

• Drafts new vgui_support API and implements it.
• Adds preliminary VGUI2 support by @kungfulon

[Velaron]

At least on Windows, you also need icudt.dll, or CEF errors out

[a1batross]

I need to stub chromehtml API, so we don't have this heavy dependency.

[mittorn]

just generate .so with same symbols as cef have. This fixes GS without chromehtml

[a1batross]

@mittorn mods should never load chromehtml.so, and in practice never do.

It's much easier to add chromehtml interface to vgui_support and return it in CreateInterface.