Port support for partial values from upstream

[pawelprazak]

We are not requesting this feature from the engine, since we pass supportsPartialValues = false

We might actually support this already or be very close to supporting this, but we need to verify and enable the feature in requests.

The upstream implementation for reference:

• https://github.com/pulumi/pulumi/issues/3455
• https://github.com/pulumi/pulumi/pull/3327/files

[lbialy]

Isn't this connected to #497 and #432?

[pawelprazak]

I haven't investigated what this missing feature is about, so I don't know. I've just noticed we don't support it.