local variables are evaluated before their dependencies from data source have been computed

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#### Overview of the Issue

I have a complex packer build "script", where i have a data source that fetches data from a website. I then have `locals` sections with local variables that reference this data source, and these locals are then referenced in other locals, which in turn are referenced in builders.

I'm seeing that sometimes the builds/sources are evaluating the locals before the root data source has been started, resulting in e.g.:

`This object does not have an attribute named "vm_name".`

I would have expected any evaluation of expressions like `vm_name = local.vm_name` on a source to be deferred until all the dependent variables, including data sources, have been resolved. Is this not the case?

### Packer version

Packer v1.12.0