Feature/preview-update

[SimonDarksideJ]

Summary

Restructured the Platformer2D project as it wouldn't open in Visual Studio and updated it to the slnx format

Also updated all samples (not tutorial) to 3.8.5-preview.* so they get and test on the latest preview.

[CartBlanche]

The other reason why this format is annoying:
Platformer2D/Windows/Windows.csproj
which the previous format also had the issues with, before I changed it to:
Platformer2D/Windows/Platformer2D.csproj
was that when building from VSCode and in particular when running builds from the command line:
dotnet build or dotnet run --project commands
with
dotnet build Platformer2D/Windows/Windows.csproj`

if I want to now build for another platform I have to change the same place twice. eg.

dotnet build Platformer2D/Android/Android.csproj

While if the structure was

dotnet build Platformer2D/Windows/Platformer2D.csproj

you literally have to change 1 thing:

dotnet build Platformer2D/Android/Platformer2D.csproj

It literally halved the amount of typing you had to do when building for a different platform.
The less typing format could have been kept and just the slnx updated and things would have just worked for everyone rather than change sln as well as the build scripts and the command lines builds wouldn't be annoying again.

I can create a new branch with those changes and I'll remember to test the slnx builds this time :)

[SimonDarksideJ]

If you can test from this PR with an updated layout @CartBlanche , I'm all ears. Just make sure the final solution is readable by VSCode or Visual Studio, as both complained about being able to open the solution.

Should we merge this PR to restore the Platformer, or wait for your update?