Engine: increase the cap of active script instances to 1024

This has an effect only on resolved bytecode created at runtime, which is never serialized. Thus there's no backwards compatibility issue.

Engine/script/cc_instance.h

@@ -44,12 +44,13 @@ using namespace AGS;
 #define MAX_CALL_STACK      128
 #define MAX_FUNCTION_PARAMS 20
 
-// 256 because we use 8 bits to hold instance number
-#define MAX_PRIMARY_INSTANCES 256
-
-#define INSTANCE_ID_SHIFT 24LL
-#define INSTANCE_ID_MASK  0x00000000000000ffLL
-#define INSTANCE_ID_REMOVEMASK 0x0000000000ffffffLL
+// We use 10 bits to hold instance IDs ORed with op-code
+#define INSTANCE_ID_SHIFT       22LL
+#define INSTANCE_ID_MASK        0x00000000000003FFLL
+#define INSTANCE_ID_REMOVEMASK  0x00000000003FFFFFLL
+// This gives us 1024 unique instance IDs
+// NOTE: these are given to the primary instances only, not forks
+#define MAX_PRIMARY_INSTANCES   1024
 
 // Script executor debugging flag:
 // enables mistake checks, but slows things down!