unify(worldbuilder): Move unified WorldBuilder to Core

[OmarAglan]

What changed

• Moved the unified WorldBuilder implementation and shared resources to Core/Tools/WorldBuilder.
• Added the corei_worldbuilder interface target.
• Reduced the Generals and Zero Hour WorldBuilder directories to thin executable wrappers.
• Preserved both game-specific splash bitmaps and selected them through the target's game compile definition.

Why

After the two implementations are synchronized, keeping duplicate source trees creates unnecessary drift. Core now owns the shared implementation while each game retains its target name, dependencies, output name, and compile definition.

Impact

Generals and Zero Hour compile the same Core WorldBuilder sources with their respective RTS_GENERALS or RTS_ZEROHOUR definition.

Validation

• CMake configure and generation succeeded for the shared interface and both wrappers
• Generated resource rules contain the correct game compile definition
• Resource preprocessing selects WorldBuilderV.bmp for Generals and WorldBuilderZH.bmp for Zero Hour
• Core CMake manifest contains all 198 source/header files
• git diff --check
• Exactly one commit relative to the WorldBuilder merge branch

Full MSVC/MFC compilation was not available in the local environment because cl.exe and msbuild.exe are absent.

Stack

3 of 3. Depends on TheSuperHackers#3025 (unify/worldbuilder-merge).