GDScript: Add limit to call depth

The hard limit is set at 2048 depth which seems sensible between
legitimate recursive calls while still avoiding a crash because of a
stack overflow in most of the cases.

Note that it is still possible to reach the stack limit and get an
overflow before reaching a call depth. This is intended as a half-way
measure to stop crashing in most cases, since there's no reliable nor
portable way to check the amount of stack memory left.

modules/gdscript/gdscript_function.h

@@ -544,6 +544,8 @@ private:
 #endif
 
 public:
+	static constexpr int MAX_CALL_DEPTH = 2048; // Limit to try to avoid crash because of a stack overflow.
+
 	struct CallState {
 		GDScript *script = nullptr;
 		GDScriptInstance *instance = nullptr;