Kernel: Add some InodeVMObject type assertions in Region::clone()

Let's make sure that we're never cloning shared inode-backed objects
as if they were private, and vice versa.

Kernel/VM/SharedInodeVMObject.h

@@ -42,6 +42,8 @@ public:
     virtual NonnullRefPtr<VMObject> clone() override;
 
 private:
+    virtual bool is_shared_inode() const override { return true; }
+
     explicit SharedInodeVMObject(Inode&, size_t);
     explicit SharedInodeVMObject(const SharedInodeVMObject&);