Expose FBO aspect

So we can customize the 3d mode if desired.

src/raylib.h

@@ -988,6 +988,7 @@ RLAPI int GetScreenWidth(void);                                   // Get current
 RLAPI int GetScreenHeight(void);                                  // Get current screen height
 RLAPI int GetRenderWidth(void);                                   // Get current render width (it considers HiDPI)
 RLAPI int GetRenderHeight(void);                                  // Get current render height (it considers HiDPI)
+RLAPI float GetCurrentAspect();                                   // Get current aspect (from the current FBO)
 RLAPI int GetMonitorCount(void);                                  // Get number of connected monitors
 RLAPI int GetCurrentMonitor(void);                                // Get current connected monitor
 RLAPI Vector2 GetMonitorPosition(int monitor);                    // Get specified monitor position

src/rcore.c

@@ -788,6 +788,12 @@ int GetRenderHeight(void)
     return height;
 }
 
+// Get current aspect (from the current FBO)
+float GetCurrentAspect()
+{
+    return (float)CORE.Window.currentFbo.width/(float)CORE.Window.currentFbo.height;
+}
+
 // Enable waiting for events on EndDrawing(), no automatic event polling
 void EnableEventWaiting(void)
 {