Access Project Solutions

I'm trying to write an extension which rebuilds all Project Solutions.
According to the official docs it's done using querySpace and RebuildAsync.
One of the Github Issues here suggests that
one can also access all Solutions using querySpace, like:

var solutions = await querySpace
     .Solutions

I'm trying this on the default Extensibility Template with the following code:

public override async Task ExecuteCommandAsync(IClientContext context, CancellationToken cancellationToken)
{
        var result = await querySpace.Solutions
                .RebuildAsync(cancellationToken);
}

However, querySpace throws an error, not appearing in the current context.

Could it be that docs and its features are out of sync, as of VS Version 17.14?

Start with the default Extensibility Template's ExecuteCommandAsync entry point and reproduce the querySpace.Solutions.RebuildAsync call in Visual Studio 17.14. Compare the available context with the official action-query documentation and the referenced issue 392. Done means confirming whether this API is supported in the template and documenting the correct behavior or the documentation mismatch.