LibGUI: Take ProcessManager's process view and turn it into GTableView.

Make it sufficiently generic that it can be reused for any table data. :^)

LibGUI/GTableView.h

@@ -0,0 +1,34 @@
+#pragma once
+
+#include <LibGUI/GWidget.h>
+#include <AK/Function.h>
+#include <AK/HashMap.h>
+
+class GScrollBar;
+class GTableModel;
+
+class GTableView : public GWidget {
+public:
+    explicit GTableView(GWidget* parent);
+    virtual ~GTableView() override;
+
+    virtual int header_height() const { return 16; }
+    virtual int item_height() const { return 16; }
+
+    void set_model(OwnPtr<GTableModel>&&);
+    GTableModel* model() { return m_model.ptr(); }
+    const GTableModel* model() const { return m_model.ptr(); }
+
+    void did_update_model();
+
+private:
+    virtual void paint_event(GPaintEvent&) override;
+    virtual void resize_event(GResizeEvent&) override;
+    virtual void mousedown_event(GMouseEvent&) override;
+
+    int item_count() const;
+    Rect row_rect(int item_index) const;
+
+    GScrollBar* m_scrollbar { nullptr };
+    OwnPtr<GTableModel> m_model;
+};