Add msdia140.dll for arm64

[SaraEmilyBergman]

Currently the msdia140.dll is only imported for x64 and x86, not arm64 (although msdia140.dll for arm64 exists):
Microsoft.TestPlatform.TestHost.nuspec.

This could cause a degraderad debugging experience on arm64 machines and I therefore suggest adding the msdia140.dll for arm64 as well.