[MSPAINT] Avoid flickering when resizing (#5144)

- Add CPaletteWindow::OnEraseBkgnd to avoid flickering.
- Add getColorBoxRect and drawColorBox helper functions to draw a color box.
- Add CPaletteWindow::DoHitTest helper function to do a hit test.
- Improve CPaletteWindow::OnPaint by using a memory bitmap.
- Improve readability of CMainWindow::alignChildrenToMainWindow.
CORE-18867

base/applications/mspaint/toolbox.h

@@ -9,6 +9,12 @@
 
 #pragma once
 
+#define TOOLBAR_ROWS        8
+#define TOOLBAR_COLUMNS     2
+#define CXY_TB_BUTTON       25
+#define CX_TOOLBAR          ((TOOLBAR_COLUMNS * CXY_TB_BUTTON) + 2)
+#define CY_TOOLBAR          ((TOOLBAR_ROWS * CXY_TB_BUTTON) + 2)
+
 class CToolBox : public CWindowImpl<CToolBox>
 {
 public: