FileManager: Port to GTableModel/GTableView.

Replace the custom DirectoryView widget with a GTableView subclass.
This was pleasantly straightforward and it's so cool seeing the huge
increase in app quality from GTableView. :^)

Applications/FileManager/DirectoryTableModel.h

@@ -0,0 +1,62 @@
+#pragma once
+
+#include <LibGUI/GTableModel.h>
+#include <sys/stat.h>
+
+class DirectoryTableModel final : public GTableModel {
+public:
+    DirectoryTableModel();
+    virtual ~DirectoryTableModel() override;
+
+    enum Column {
+        Icon = 0,
+        Name,
+        Size,
+        UID,
+        GID,
+        Permissions,
+        Inode,
+        __Count,
+    };
+
+    virtual int row_count() const override;
+    virtual int column_count() const override;
+    virtual String column_name(int column) const override;
+    virtual ColumnMetadata column_metadata(int column) const override;
+    virtual GVariant data(int row, int column) const override;
+    virtual void update() override;
+    virtual void activate(const GModelIndex&) override;
+
+    String path() const { return m_path; }
+    void open(const String& path);
+    size_t bytes_in_files() const { return m_bytes_in_files; }
+
+private:
+    struct Entry {
+        String name;
+        size_t size { 0 };
+        mode_t mode { 0 };
+        uid_t uid { 0 };
+        uid_t gid { 0 };
+        ino_t inode { 0 };
+        bool is_directory() const { return S_ISDIR(mode); }
+    };
+
+    const Entry& entry(int index) const
+    {
+        if (index < m_directories.size())
+            return m_directories[index];
+        return m_files[index - m_directories.size()];
+    }
+    const GraphicsBitmap& icon_for(const Entry& entry) const;
+
+    String m_path;
+    Vector<Entry> m_files;
+    Vector<Entry> m_directories;
+    size_t m_bytes_in_files;
+
+    RetainPtr<GraphicsBitmap> m_directory_icon;
+    RetainPtr<GraphicsBitmap> m_file_icon;
+    RetainPtr<GraphicsBitmap> m_symlink_icon;
+    RetainPtr<GraphicsBitmap> m_socket_icon;
+};