Adding walkValidate to the EvalTree operations, and removing the
walkValidate guard from the Interpolater.valueModuleVar allows the
values to be interpolated for Validate.
Variables weren't being interpolated during the Input phase, causing a
syntax error on the interpolation string. Adding `walkInput` to the
EvalTree operations prevents skipping the interpolation step.
This commit forward ports the changes made for 0.6.17, in order to store
the type and sensitive flag against outputs.
It also refactors the logic of the import for V0 to V1 state, and
fixes up the call sites of the new format for outputs in V2 state.
Finally we fix up tests which did not previously set a state version
where one is required.
