LibJS: Add Bytecode::Executable::dump()

Let's have a helper for producing a consistent executable dump instead
of repeating the logic in multiple places.

Userland/Libraries/LibJS/Bytecode/Executable.h

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/NonnullOwnPtrVector.h>
+#include <LibJS/Bytecode/BasicBlock.h>
+#include <LibJS/Bytecode/StringTable.h>
+
+namespace JS::Bytecode {
+
+struct Executable {
+    NonnullOwnPtrVector<BasicBlock> basic_blocks;
+    NonnullOwnPtr<StringTable> string_table;
+    size_t number_of_registers { 0 };
+
+    String const& get_string(StringTableIndex index) const { return string_table->get(index); }
+
+    void dump() const;
+};
+
+}