[VS 15.6 RTW] alt-up/down arrows do not reposition file for legacy projects

[vsfeedback]

VS 15.6 preview6

1. Create a .NET Framework-based F# project
2. Alt+up/Alt+Down on a file (Program.fs)

Expected: files move up/down
Actual: They don't

This issue has been moved from https://developercommunity.visualstudio.com/content/problem/204016/vs-156-preview6-alt-updown-arrows-do-not-repositio.html
VSTS ticketId: 572477
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[cartermp]

It's unclear if this is something we can adjust here, in dotnet-project-system, or in the VS editor itself. Either way, the root of the issue is that we assigned hotkeys to .NET Core SDK-based projects for Alt+Up/Alt+Down. This apparently removed the cability from legacy projects because you can only have one key binding per editor context.

[TIHan]

We have a possible solution to this.

We need to create an interface that we export an implementation to execute the legacy VisualFSharp commands for MoveUp/Down. This interface will live in VisualFSharp.

Using COM definitions, we can have the same interface in dotnet/project-system and get an instance through MEF. With this instance, we can execute the legacy MoveUp/Down once we see a hierarchy that is not CPS based.

[cartermp]

Labeling and adding to the 15.6 milestone. This won't block the release since we're so soon to shipping, but we're going to target a servicing release.

[cartermp]

This has been fixed in dotnet/project-system#3331 and merged into a validation build. Servicing fix should be out fairly soon.