If an update fails, update any stack outputs that were updated, but
otherwise leave existing stack outputs as-is. In other words, don't
delete stack outputs if the stack didn't successfully run to completion.
Implementation note: when we receive a RegisterResourceOutputsEvent for
the stack resource, we defer processing it until the end of the
deployment, to know whether the deployment ran to completion without
errors.
Fixes#14621
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Co-authored-by: Thomas Gummerer <t.gummerer@gmail.com>