Add concept of size increments to windowing system.

Use this to implement incremental resizing for Terminal so that we only
ever resize to fit a perfect number of rows and columns.

This is very nice. :^)

Applications/Terminal/Terminal.cpp

@@ -785,7 +785,6 @@ void Terminal::force_repaint()
 {
     for (int i = 0; i < m_rows; ++i)
         line(i).dirty = true;
-    m_need_full_flush = true;
     update();
 }
 
@@ -795,3 +794,9 @@ void Terminal::resize_event(GResizeEvent& event)
     int new_rows = event.size().height() / m_line_height;
     set_size(new_columns, new_rows);
 }
+
+void Terminal::apply_size_increments_to_window(GWindow& window)
+{
+    window.set_size_increment({ font().glyph_width(), m_line_height });
+    window.set_base_size({ m_inset, m_inset });
+}

Applications/Terminal/Terminal.h

@@ -21,6 +21,8 @@ public:
     void flush_dirty_lines();
     void force_repaint();
 
+    void apply_size_increments_to_window(GWindow&);
+
 private:
     virtual void event(GEvent&) override;
     virtual void paint_event(GPaintEvent&) override;

Applications/Terminal/main.cpp

@@ -92,6 +92,7 @@ int main(int argc, char** argv)
     window->set_has_alpha_channel(true);
     window->set_main_widget(&terminal);
     window->move_to(300, 300);
+    terminal.apply_size_increments_to_window(*window);
     window->show();
 
     auto menubar = make<GMenuBar>();