VisualBasicPackage must be constructed on the main thread

[sharwell]

This package was incorrectly set as AllowsBackgroundLoad=true when the constructor contained a UI-affinitized operation. We attempted to moved the operation to InitializeAsync instead, but it did not work (exception in a comment below). Instead, we have marked this package as requiring the UI thread for construction.

Fixes AB#1745017

[sharwell]

Integration tests are failing to create VB projects:

System.ArgumentException: Value does not fall within the expected range.
   at Microsoft.VisualStudio.CommonIDE.Solutions.Interop.IVsNativeEnvironmentInternal.WizLoadAndRunFile(String pwszWizard, String pwszDestination, Boolean bCloseSolution, Boolean bRunSilent, Array psaCustomParams, String pwszFrameworkVersion)
   at Microsoft.VisualStudio.CommonIDE.Solutions.Solution.<>c__DisplayClass417_0.<Microsoft.VisualStudio.Shell.Interop.IVsSolution6.AddNewProjectFromTemplate>b__0()
   at Microsoft.VisualStudio.CommonIDE.Solutions.HResultExtensions.ExToHr(Action action)
   at System.Runtime.InteropServices.Marshal.ThrowExceptionForHRInternal(Int32 errorCode, IntPtr errorInfo)
   at Microsoft.VisualStudio.ErrorHandler.ThrowOnFailure(Int32 hr)
   at Microsoft.VisualStudio.Extensibility.Testing.SolutionExplorerInProcess.<AddProjectAsync>d__14.MoveNext() in /_/src/VisualStudio/IntegrationTest/New.IntegrationTests/InProcess/SolutionExplorerInProcess.cs:line 221
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at Roslyn.VisualStudio.NewIntegrationTests.Workspaces.WorkspaceBase.<OpenCSharpThenVBSolution>d__4.MoveNext() in /_/src/VisualStudio/IntegrationTest/New.IntegrationTests/Workspace/WorkspaceBase.cs:line 56
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at Xunit.Threading.InProcessIdeTestInvoker.<>c__DisplayClass6_1.<<InvokeTestMethodAsync>b__1>d.MoveNext()