Update Visual Studio settings from SDL2-times

[Starbuck5]

Currently, the Visual Studio project here only builds the SINEWAVE and RAW decoders. This adjusts the settings to build all the normal decoders by adjusting the names and includes that haven't been updated since the big rewrite.

It also removes the SDL3 subproject, which was removed from the repo in January. 4d068ed

• I was trying to use only includes from the external/ directory to avoid the need for includes inside the Visual Studio project folder, but I couldn't get that to work for opusfile and wavpack. I tried using the xyz_HEADER defines to redefine the headers to "<wavpack.h> instead of <wavpack/wavpack.h>", for example, and then added external/wavpack/include as an additional directory, but this didn't work for an unknown reason.
• For some reason, I wasn't able to get a debug x64 build to work, but I adjusted its settings the same way as everything else