Add KSPAssembly, repair version-gen, cross platform build

[HebaruSan]

• KSPAssembly is now added to AssemblyInfo.cs so other mods (such as SmartTank) can use KSPAssemblyDependency to indicate a dependency on this mod
• Since it looks like this is generated from AssemblyInfo.in, this is updated as well
• The version-gen script is updated to generate correct output in the right places
  • Tie::IxHash is used to print the keys in the right order
  • The output path of the version file is updated to where it lives now
  • Compatibility in the script is updated to 1.8.1–1.12.99
  • The new @VERSION_MAJOR@, @VERSION_MINOR@, and @VERSION_MAJOR_FIRST@ variables in AssemblyInfo.in are now substituted
• The version file is regenerated by the script with more consistent formatting
  • Indenting with 4 spaces
  • No spaces before colons
  • No quotes around numbers
• The Makefile no longer references two files that were deleted
• The Makefile now uses the current C# compiler csc rather than the very old and deprecated gmcs
• The csproj's Windows-specific xcopy <PostBuildEvent/> is replaced with a cross-platform <Target/> that uses <Copy/> to do the same thing but works on all platforms

Tagging @NathanKell and @StonesmileGit in case GitHub doesn't send notifications for this.

[siimav]

Thanks for this. Unfortunately the effort you put into the perl script is a bit redundant since ultimately we're going to replace that with the GH Actions we already have in place for RO, RP-1 etc.

[HebaruSan]

Unfortunately the effort you put into the perl script is a bit redundant since ultimately we're going to replace that with the GH Actions we already have in place for RO, RP-1 etc.

So much the better; it's weird to see Perl in 2022. But if it's still there and it looks to the casual observer like the proper way to maintain AssemblyInfo.cs, then it might as well work.