Optimize multiple incax* and incax*/ldaxi

- Group multiple calls to incax* and decax* into a single one
- Replace incaxN/jsr ldaxi with ldy #N+1/jsr ldaxidx

Fixes #2055

test/val/bug2205.c

@@ -0,0 +1,20 @@
+#include "unittest.h"
+
+struct Object
+{
+    int a;
+    int data[10];
+};
+
+struct Object object_data = { 0x0102, {0x0304, 0x0506, 
+                             0x0708, 0x090A, 0x0B0C,
+                             0x0D0E, 0x0F10, 0x1112,
+                             0x1314, 0x1516}};
+
+TEST
+{
+    struct Object *o = &object_data;
+    ASSERT_IsTrue(o->a == 0x0102, "Wrong value for a");
+    ASSERT_IsTrue(o->data[2] == 0x0708, "Wrong value for data[2]");
+}
+ENDTEST