Use the global providers.SchemaCache and update all schema access to the
providers.Schemas, except where the provider.GetProviderSchemaResponse
type name would be expected.
Some tests that reuse provider factories needed a little more careful
handling. Change the fixed func to only reset the provider on the first
call.
This is part of a general effort to move all of Terraform's non-library
package surface under internal in order to reinforce that these are for
internal use within Terraform only.
If you were previously importing packages under this prefix into an
external codebase, you could pin to an earlier release tag as an interim
solution until you've make a plan to achieve the same functionality some
other way.
