Making TeamExplorerServiceHolder testable

[shana]

This makes TeamExplorerServiceHolder testable by moving/abstracting all the dependent VS types.

This also reverts the change to have GitHub.TeamFoundation.15 reference Shell.15 - we rely on types from Shell.14 in GitHub.Exports and other areas (Shell.14 is available in VS 2017), namely UIContextChangedEventArgs.

[grokys]

When running this I get:

Exception thrown: 'GitHub.GitHubLogicException' in GitHub.Exports.dll

Additional information: Could not locate view model for GitHubPane.

[jcansdale]

This also reverts the change to have GitHub.TeamFoundation.15 reference Shell.15

The problem is that Microsoft.TeamFoundation.Git.Provider, Version 15.0.0.0 (which we reference from GitHub.TeamFoundation.15), references the Microsoft.VisualStudio.Shell.15.0 assembly.

This causes the following warning.

C:\Program Files (x86)\MSBuild\14.0\bin\Microsoft.Common.CurrentVersion.targets(1820,5):
warning MSB3277: Found conflicts between different versions of the same dependent assembly that
could not be resolved.  These reference conflicts are listed in the build log when log verbosity is set to detailed.
[C:\source\github.com\github\VisualStudio\src\GitHub.TeamFoundation.15\GitHub.TeamFoundation.15.csproj]

These warnings can be difficult to track down and it isn't at all clear what the issue is whether it's serious or not.

[jcansdale]

I keep getting the following on this branch:

I wonder what's going on?

[shana]

This should be working now, MEF crashes are fixed.

Also, this branch is now loading the following DLLs up front when starting VS in Team Explorer Home:

Note that GitHub.Exports.Reactive, GitHub.UI.Reactive and GitHub.Extensions.Reactive are not on the list, which is good! But rx is still getting loaded, probably via GitHub.App, so we should continue spelunking to find out what's loading GitHub.App so we stop doing that (this might be the credential handler, in which case #1277 might fix that.

[grokys]

Approved, with one nit.

[grokys]

IGitRepositoryInfoExtensions.ToModel is an extension method so why not just say x.ToModel()?

[grokys]

Fixed the nit so 👍