Addendum to #2635. Add support for multi-viewports in SDL+DX!! example. making all Win32-centric back-ends handle PlatformHandleRaw. Using the field to use/store the HWND for internal purpose in SDL/GLFW back-ends. (#1542)

Examples: SDL+DX11: Changelog, readme, batch files, fixed vcxproj, minor stylistic fixes + minor sync of other main.cpp files. (#2632)

Implement SDL/dx11 sample