DTE2 members to implement in new Extensibility Model

[LeeMSilver]

Per issue #352 my extension may not be able to use await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync(); and therefore not be convertible to the new Extensibility Model (EM).

I only use that method for accessing some DTE2 members and its use is the reason that my extension is in-proc. If the EM could implement the following DTE2 members my extension conversion can continue (and be out-of-proc.)

• DTE.ExecuteCommand("File.Close") and DTE.ExecuteCommand("File.FormatDocument") -see issue Request for a Close() method #337.

• `DTE,StatusBar

• DTE.ExecuteCommand() -used in a number of places (e.g. "EditorContextMenus.FileHealthIndicator.RunCustomCodeCleanup") multiple times per command.

How they are implemented (e.g. in their own class, as extension methods, etc.) is of no concern, nor is it a concern if any of them have to use await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync(); as long as they return on the calling thread (or any thread, so long as execution can continue and possibly invoke DTE.ExecuteCommand() multiple times.