[UXTHEME] Greatly reduce the number of times we open the theme data for the non client area. - Implement OTD_NONCLIENT for OpenThemeDataEx and OpenThemeDataFromFile. - Open the WINDOW or the SCROLLBAR theme classes only when needed. Use OpenThemeDataEx instead of the internal MSSTYLES_OpenThemeClass. Cache the open theme in the WND_DATA for later use.
[UXTHEME] -Rename WND_CONTEXT to WND_DATA to avoid confusion with the DRAW_CONTEXT. The WND_DATA is information valid throughout the life of a window and DRAW_CONTEXT is information throughout a draw operation in the non client area of the window.