This change fixes up a few things so that updates correctly deal
with output properties. This involves a few things:
1) All outputs stored on the pre snapshot need to get propagated
to the post snapshot during planning at various points. This
ensures that the diffing logic doesn't need to be special cased
everywhere, including both the Lumi and the provider sides.
2) Names are changed to "input" properties (using a new `lumi` tag
option, `in`). These are properties that providers are expected
to know nothing about, which we must treat with care during diffs.
3) We read back properties, via Get, after doing an Update just like
we do after performing a Create. This ensures that if an update
has a cascading impact on other properties, it will be detected.
4) Inspecting a change, prior to updating, must be done using the
computed property set instead of the real one. This is to avoid
mutating the resource objects ahead of actually applying a plan,
which would be wrong and misleading.
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