LibJS: Add six typed arrays (signed and unsigned 8/16/32-bit)

This patch adds six of the standard type arrays and tries to share as
much code as possible:

- Uint8Array
- Uint16Array
- Uint32Array
- Int8Array
- Int16Array
- Int32Array

Libraries/LibJS/Runtime/Object.h

@@ -129,6 +129,7 @@ public:
     virtual bool is_array_iterator_object() const { return false; }
     virtual bool is_lexical_environment() const { return false; }
     virtual bool is_global_object() const { return false; }
+    virtual bool is_typed_array() const { return false; }
 
     virtual const char* class_name() const override { return "Object"; }
     virtual void visit_edges(Cell::Visitor&) override;