Update tests in library/src/tests to refer to Std.* instead of Microsoft.Quantum.*

[fedimser]

Microsoft.Quantum.* is deprecated.

In all tests in library/src/test we should refer to operations by prefixing them with "Std" instead "Microsoft.Quantum". For example, Microsoft.Quantum.Convert should be replaced with Std.Convert. This applies to tests and comments.

See library/std/src/legacy_api.qs for how those names are re-exported. Also check if there are other locations in QDK where we refer to deprecated namespaces and do changes there as well.