Instead of requiring a plugin host for package loading in the HCL2
binder, define a much narrower interface that exposes the ability to
fetch the schema for a package at a specific version. This interface is
defined in the schema package, which also exposes a caching loader that
is backed by provider plugins.
These changes also add some convenience methods to `*schema.Package` for
fast access to particular resources and functions.
Related to #1635.
- Move the implementation of loadPackageSchema into a method on
PackageCache
- Protect the cache with synchronization primitives to enable
concurrency in downstream consumers
- Use jsoniter to deserialize schemas
