"Use explicit type instead of 'var'" should opt for adding a "using" instead of fully qualifying

[davkean]

Use explicit type will fully qualify a type if there is not already a using in scope. This is annoying if you never want a fully qualified type.

This in contrast to the spell checker, which does opt for a using vs fully qualifying:

[CyrusNajmabadi]

Seems reasonable. Open question about priority of the options shown to the user. When a fix adds a using as a side effect, we generally deprioritize those (which has the added benefit of making the user have to go explicitly choose it).

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Alternatively, we could consider a feature which offers to add a using and simplify a type name when on a fully qualified type. This would require two invocations in a situation like this. However, it would be more flexible and would also just add a useful feature for people going through code with fully qualified type-names that they wanted to clean up.

[davkean]

While the later code fix would be helpful in some situations, I still think you should add it by default. There's also other code fixes that also automatically add a using, such as implement interface, it would be tedious to have to run another code fix just to fix up all these cases.

[Neme12]

A separate refactoring would definitely be nice and useful on its own.

[davkean]

I just ran into this again: dotnet/project-system#3502. It's pretty painful to manually have to fix these cases.