The main significant change here is that the package name for the proto
definition is "tfplugin5", which is important because this name is part
of the wire protocol for references to types defined in our package.
Along with that, we also move the generated package into "internal" to
make it explicit that importing the generated Go package from elsewhere is
not the right approach for externally-implemented SDKs, which should
instead vendor the proto definition they are using and generate their
own stubs to ensure that the wire protocol is the only hard dependency
between Terraform Core and plugins.
After this is merged, any provider binaries built against our
helper/schema package will need to be rebuilt so that they use the new
"tfplugin5" package name instead of "proto".
In a future commit we will include more elaborate and organized
documentation on how an external codebase might make use of our RPC
interface definition to implement an SDK, but the primary concern here
is to ensure we have the right wire package name before release.
Even if a provider doesn't indicate a specific attribute as the cause of
a resource operation error, we know the error relates to some aspect of
the resource, so we'll include that approximate information in the result
so that we don't produce user-hostile error messages with no context
whatsoever.
Later we can hopefully refine this to place the source range on the header
of the configuration block rather than on an empty part of the body, but
that'll require some more complex rework here and so for now we'll just
accept this as an interim state so that the user can at least figure out
which resource block the error is coming from.
Managing which function need to be shared between the terraform plugin
and the helper plugin without creating cycles was becoming difficult.
Move all functions related to converting between terraform and proto
type into plugin/convert.
