Project-system: Add an API that lets consumers wait on language service to be up-to-date with a given project version

[davkean]

We need an API that lets consumers wait on the language service to be up-to-date with a given project version, similar to IProjectTreeService.PublishTree:

```c#
Task PublishLatestAsync(
CancellationToken cancellationToken = default(CancellationToken));

Task PublishAsync(
IImmutableDictionary minimumRequiredDataSourceVersions,
CancellationToken cancellationToken = default(CancellationToken));
```

This lets services such as CodeModel provider to block this before returning a CodeModel item, or the renamer to block on this attempting to rename. Also lets us block VS integration tests on this work before attempting to test state.

Without this, it's impossible to know when ProjectItem.CodeModel is going to return a result.

[AbhitejJohn]

Happy to test this out when we have one.

[AbhitejJohn]

@davkean : Did we get a chance to schedule this work in yet...

[davkean]

We're doing this as part of the language service hookup rewrite in 15.8. First part is in review, but we've only started on 15.8 this week. We're at least a sprint away from it.

[japj]

Any update on this? It seems this is a blocking issue for
https://developercommunity.visualstudio.com/content/problem/145930/create-unit-test-context-menu-missing-net-core-pro.html

[Pilchie]

Note also that as part of this work we should use this API to push information to the VS Platform's new Operation Progress API so that we can track the async initialization.

[kristianjaeger]

@davkean Any updates on this? Thank you.

[AliBayatGH]

It is December 30, 2018, and we are still on 15.9.4 with no create unit testing on .NET Core projects.

[tolgabalci]

Looking forward to getting the option for "Create Unit Tests" for our .Net Core apps. This is a great time saver and helps Jr developers be more comfortable with creating unit tests.

[kristianjaeger]

@Pilchie or @davkean Any updates on this? From May 2018 to January 2019 is a long sprint ;) . Thank you.

[davkean]

Appreciate your patience here, but due to the nature of software development it is hard to give a timeframe especially given the feature it was blocked on, only got to the point 5 minutes of ago of being ready to merge. We have tentatively put this in 16.1 timeframe but its priority is behind our focus for that release; .NET Core 3.0.

[kristianjaeger]

Thanks for the update. I think that folks are really looking forward to having feature parity for this. Cheers.

[iWangJiaxiang]

Appreciate your patience here, but due to the nature of software development it is hard to give a timeframe especially given the feature it was blocked on, only got to the point 5 minutes of ago of being ready to merge. We have tentatively put this in 16.1 timeframe but its priority is behind our focus for that release; .NET Core 3.0.

Hello, VS 2019 16.1.0 has been released and the feature to create tests for .Net Core is still not available?

[opis-mark]

It looks as though this issue has been moved to 16.2 milestone. Is there any indication as to whether or not it will gain enough traction to actually be included in 16.2? I would just like to add a vote for the ability to create tests .Net Core projects as well.

[duaneking]

Any updates?