Add a smoke test for constant slot optimization

Author: kateinoigakukun

Tests/WasmKitTests/ExtraSuite/const_slot.wast

@@ -0,0 +1,15 @@
+(module
+  (func (export "check") (param i32) (result i32)
+    ;; Enough to reach the limit of constant slots
+    (drop (i32.const 1))
+    (drop (i32.const 2))
+    (drop (i32.const 3))
+    (drop (i32.const 4))
+    (drop (i32.const 5))
+    (drop (i32.const 6))
+    (i32.add (local.get 0) (i32.add (i32.const 1) (i32.const 1)))
+  )
+)
+
+(assert_return (invoke "check" (i32.const 3)) (i32.const 5))
+