Port output serialization tests

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Issue details

Capturing a reminder to test out Output value serialization from a Slack thread.

There is rather an extensive suite of tests in Go, we need to eventually match most of this behavior:

https://github.com/pulumi/pulumi/blob/f989e1cc9d639feb045469b536fac8944394fbc1/sdk/go/common/resource/plugin/rpc_test.go#L481

There are especially pertinent cases that may be a bit under-documented but important:

• If keepOutputs=true feature is on, Outputs with additional data (deps, secret, unknown) serialize into a special Struct shape with a type marker, and explicit dependency lists
• Outputs without additional data serialize just as their plain value would
• Unknown outputs serialize to a special computed sentinel
• TBD - verify how secret outputs serialize

Based on our discussions we currently think this all can work with deleting Input<T> type and simply focusing on the Output<T> type. There may be some degenerate cases like Output<Output<T>> values that serialize ambiguously and don't quite turn around but we may be okay with that since these should not arise in our use cases.

Affected area/feature

Start with the referenced Go test suite at sdk/go/common/resource/plugin/rpc_test.go around line 481 and locate the corresponding Output serialization code and tests in pulumi-java. Compare the Java behavior with the listed keepOutputs, dependency, secret, unknown, and plain-value cases. Done means the relevant Java tests cover the agreed cases, including the still-undetermined secret-output behavior.