Utilize Fsc args in msbuild analyze if available

[TheAngryByrd]

This kind of revitalizes https://github.com/ionide/FSharp.Analyzers.SDK/pull/164, but this takes a slightly different approach.

• Instead of trying to do a DesignTimeBuild within msbuild, it will try to run after a CoreCompile/AfterBuild target actually runs.
• This uses the RunAnalyzer or RunAnalyzersDuringBuild (see Roslyn variables) to determine if it should run or not.
• This will skip the FsharpAnalyzerAfterBuild target if CoreCompile does not produce FscArgs. However someone can use FSharpAnalyzers_AlwaysRunAfterBuild to always run after a build, still using Ionide.ProjInfo as before to do design time builds.

[nojaf]

Wow, this looks amazing! Will play with this when I can!

[baronfel]

This follows incremental builds so it won't run unless CoreCompile produces FscArgs.

I'm hearing you say that the output Property/Item isn't being set on purely-incremental builds. I'm not sure that is expected behavior - I'd expect that an incrementally-skipped Target would emit its outputs.

[TheAngryByrd]

I'd expect that an incrementally-skipped Target would emit its outputs.

Yeah it's not really incremental usingg the Inputs/Outputs semantics, only running conditionally when FscCommandLineArgs gets set from a CoreCompile.

[TheAngryByrd]

Ok updated my comment on incremental builds, since following Inputs/Outputs would probably be too much effort.