The changes in #4004 caused old provider configuration to be used even when a provider was different between inputs and outputs, in the case that the diff returned DiffUnkown.
To better handle that case, we compute a more accurate (but still conservative) DiffNone or DiffSome so that we can ensure we conservatively update to a new provider when needed, but retain the performance benefit of not creating and configuring a new provider as much as possible.
Part of https://github.com/pulumi/pulumi-aws/issues/814.
74ffbfd9ba