games/vcmi: update the port to version 1.6.3

• VCMI mod now uses same filesystem as all mods, with all files located under `Content' directory
• Moved all PNG images from Data' directory to Sprites'
• Use TTF_Font' type provided by <SDL_ttf.h> to unbreak the build against graphics/sdl2_ttf' version 2.24.0
• Add `post-patch' target to prevent accidentally picking up Qt 6 bits if they're installed (always prefer Qt 5)

PR: 283866