LibJS/JIT: Dump disassembly of generated code using LibX86

This avoids the need for redirecting stdout to a file and using
ndisasm, which can lead to problems if other things are printed.

Userland/Libraries/LibJS/JIT/NativeExecutable.h

@@ -21,6 +21,7 @@ public:
     ~NativeExecutable();
 
     void run(VM&) const;
+    void dump_disassembly() const;
 
 private:
     void* m_code { nullptr };