jsonconfig: Improve provider configuration output

When rendering configuration as JSON, we have a single map of provider
configurations at the top level, since these are globally applicable.
Each resource has an opaque key into this map which points at the
configuration data for the provider.

This commit fixes two bugs in this implementation:

- Resources in non-root modules had an invalid provider config key,
  which meant that there was never a valid reference to the provider
  config block. These keys were prefixed with the local module name
  instead of the path to the module. This is now corrected.

- Modules with passed provider configs would point to either an empty
  provider config block or one which is not present at all. This has
  been fixed so that these resources point to the provider config block
  from the calling module (or wherever up the module tree it was
  originally defined).

We also add a "full_name" key-value pair to the provider config block,
with the entire fully-qualified provider name including hostname and
namespace.

internal/command/testdata/show-json-sensitive/output.json

@@ -164,6 +164,7 @@
         "provider_config": {
             "test": {
                 "name": "test",
+                "full_name": "registry.terraform.io/hashicorp/test",
                 "expressions": {
                     "region": {
                         "constant_value": "somewhere"