We were previously filtering out pulumi:pulumi:Stack resources
from the output of `pulumi stack`. This is perhaps the right thing
to do -- since it's just a logical container and every stack will
contain one -- but it poses problems because the overall experience
right now treats it like a resource. So filtering it is odd in
a few ways: e.g., resource counts look wrong, removing the stack
won't work because there's a hidden resource within it, etc. This
change simply lists it in the output, which seems safe to do for now.
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