[OSK] Make the buttons themed

[OSK] Make the buttons themed

Our On-Screen Keyboard has a manifest and the buttons (the ones with BS_ICON styles) aren't rendered with the specific theme as it should be but instead it takes the classic theme.

The code relies on NM_CUSTOMDRAW notification, which is more intuitive and efficient than doing owner-drawn operations as NM_CUSTOMDRAW allows the controls to use styles whereas you cannot do it on owner-drawn controls.

CORE-15965