This now uses the HCL2 parser and evaluator APIs and evaluates in terms
of a new-style *lang.Scope, rather than the old terraform.Interpolator
type that is no longer functional.
The Context.Eval method used here behaves differently than the
Context.Interpolater method used previously: it performs a graph walk
to populate transient values such as input variables, local values, and
output values, and produces its scope in terms of the result of that
graph walk. Because of this, it is a lot more robust than the prior method
when asked to resolve references other than those that are persisted
in the state.
The indent function was stripping out newlines, causing multi-element
lists and maps to be rendered incorrectly.
We were also not quoting strings in these nested structures, leading to
weird behavior if any expression punctuation or newlines were present in
these strings.
This part of Terraform will get a more serious overhaul as part of
switching to the new parser/interpreter implementation but this is a
tactical fix to make the results of this command more usable in the
short term.
