The cty change here fixes a panic situation when cty.Path.Apply is given
a null value, making it now correctly return an error.
However, the HCL2 change includes an alternative to cty.Path.Apply that
uses HCL-level rules rather than cty-level rules, so the result behaves
like an HCL expression would. Most uses of cty.Path.Apply ought to use
hcl.ApplyPath instead, to ensure that the behavior is consistent with what
users expect in the main language.
This includes the new PathSet type, which we'll use to represent the
"requires replacement" set of attribute paths coming back from providers
during planning.
This is largely minor bugfixes for issues found since we last updated the
vendoring. There are some new features here that Terraform is not yet
using and thus present little risk.
In particular this includes the HCL-JSON spec change where arrays can now
be used at any level in a block label structure, to allow for preserving
the relative order of blocks.
Martin Atkins