All ServiceLocator calls that retrieve MEF services should avoid the UI thread.

[nkolev92]

Avoid using methods that access the UI thread when request services exposed via MEF. Use free threaded calls, or ideally uses MEF composition.

This means adding a new public method in ServiceLocator

[nkolev92]

Note that this issue means reviewing methods such as:

GetInstance, GetInstanceAsync, GetInstanceSafe

[nkolev92]

NuGet/NuGet.Client#4229 seems like it has a regression, not sure why.

[nkolev92]

Actually I know why :D

The PackageSourceProvider is probably not set early enough, because it's set during the package initialization, so getting the SComponentModel likely returns null, because it used to default to return Package.GetGlobalService(typeof(TService)) as TInterface; but now it doesn't.