Kernel: Split VMObject into two classes: Anonymous- and InodeVMObject

InodeVMObject is a VMObject with an underlying Inode in the filesystem.
AnonymousVMObject has no Inode.

I'm happy that InodeVMObject::inode() can now return Inode& instead of
VMObject::inode() return Inode*. :^)

Kernel/VM/InodeVMObject.h

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <Kernel/UnixTypes.h>
+#include <Kernel/VM/VMObject.h>
+
+class InodeVMObject final : public VMObject {
+public:
+    virtual ~InodeVMObject() override;
+
+    static NonnullRefPtr<InodeVMObject> create_with_inode(Inode&);
+    virtual NonnullRefPtr<VMObject> clone() override;
+
+    Inode& inode() { return *m_inode; }
+    const Inode& inode() const { return *m_inode; }
+
+    void inode_contents_changed(Badge<Inode>, off_t, ssize_t, const u8*);
+    void inode_size_changed(Badge<Inode>, size_t old_size, size_t new_size);
+
+private:
+    explicit InodeVMObject(Inode&);
+    explicit InodeVMObject(const InodeVMObject&);
+
+    InodeVMObject& operator=(const InodeVMObject&) = delete;
+    InodeVMObject& operator=(InodeVMObject&&) = delete;
+    InodeVMObject(InodeVMObject&&) = delete;
+
+    virtual bool is_inode() const override { return true; }
+
+    NonnullRefPtr<Inode> m_inode;
+};