Remove FSharp.Editor dependency on FSharp.Language Service redux

[cartermp]

Rebase with reverted commits sucks.

This PR:

• Moves ProjectSitesAndFiles into FSharp.Editor
• Moves the remaining helper code from FSharp.LanguageService into FSharp.Editor
• Removes the dependency on FSharp.LanguageService from FSharp.Editor
• Adjusts calls in the legacy project system to call the correct ProjectSitesAndFiles code
• Adjusts legacy language service tests which only test deprecated functionality to no longer depend on FSharp.Editor
• Adjusts legacy project system tests to call the correct things
• Does minor cleanup

Tested:

• Creation of .NET Framework and .NET Core SDK-based projects
• Mixing of .NET Framework and .NET Standard projects, with references
• File ordering in the above
• New files in the above
• Script files in the above
• IDE features work in the above

There is still a possible need for an integration test which verifies that when the old project system loads a project, the language service is successfully initialized. This apparently doesn't exist in our test suite, hence #4108 ultimately failing due to lacking the correct changes to calls in the legacy project system.

[cartermp]

This is no longer WIP. I installed this PR into my F# tools and used it for a few days, and noticed that #4137 was occurring, but after @dwed confirmed that he also saw that long before this PR was ever created, I don't think that assertion is related.

This is not critical for 15.6, but I think it's definitely worth getting in for 15.7.

[dsyme]

@cartermp I seem to remember an earlier version of this causing problems - was that the scare around #4137 or did the first version really have an issue? thanks

[cartermp]

The first version did have an issue where the language service wasn't being initialized in .NET Framework projects (which CI didn't catch, heh). I fixed it here.

[dsyme]

@cartermp OK, great :)

[KevinRansom]

@dotnet-bot test this please.

[dsyme]

@cartermp After this PR the FSharp.ProjectSystem (old project system) still contains this reference:

    <ProjectReference Include="..\FSharp.LanguageService\FSharp.LanguageService.fsproj">
      <Name>FSharp.LanguageService</Name>
      <Project>{ee85aab7-cda0-4c4e-bda0-a64ccc413e3f}</Project>
      <Private>True</Private>
    </ProjectReference>

Is this intended, e.g. is there going to be multiple copies of state in FSharp.LanguageService.dll and FSharp.Editor.dll?

[cartermp]

@dsyme I could take a look at pulling out that ref today. I intended only to cut ties with FSharp.LanguageService from FSharp.Editor, but if we can completely orphan it save for unit tests then that's preferrable

[dsyme]

if we can completely orphan it save for unit tests then that's preferrable

Definitely. And if we can't I fear a bug :)

[cartermp]

So removing that reference is fine, but I did notice that #4376 shows up if I build a VSIX of the latest master into 15.6 preview 5. I haven't done itfor some time, so I have no idea if it's this or not.

[cartermp]

Confirmed that this PR does not cause #4376