Added IsMapbase() defined funtion

[Unusuario2]

This PR introduces a small utility macro IsMapbase() to improve readability and maintainability when working with Mapbase-dependent code.

Future updates will support larger mods with many Mapbase features. Using #ifdef MAPBASE everywhere can clutter the code or take multiple lines. Adding IsMapbase() gives programmers a cleaner, one-line way to check for Mapbase support.

Example:
if constexpr (IsMapbase()) { // Mapbase-specific logic }
instead of
#ifdef MAPBASE // Mapbase-specific logic #endif //MAPBASE

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