[MSPAINT] Make sizeboxes window-less (#5166)

[MSPAINT] Make sizeboxes window-less (#5166)

Reduce window controls and integrate to the canvas window.
- The sizeboxes are absorbed by canvasWindow.
- class CSizeboxWindow is deleted.
- Add enum CANVAS_HITTEST.
- Add getSizeBoxRect, getSizeBoxHitTest, and drawSizeBoxes helper functions in sizebox.cpp.
CORE-18867