test(liveshare-protocol): neutralize provider-specific fixture subjects

The recorded frames no longer name a provider-specific subject prefix; the cases keep their shape
with a neutral subject id.

packages/experimental/liveshare-protocol/tests/frames/unknown/relay-to-gateway--id-not-a-positive-integer.json

@@ -12,7 +12,7 @@
     "actor": {
       "providerId": "example",
       "tenantId": "tenant-a",
-      "subjectId": "ou_viewer"
+      "subjectId": "user_viewer"
     }
   },
   "refusal": null

packages/experimental/liveshare-protocol/tests/frames/v1/host-to-worker--add-share.json

@@ -12,7 +12,7 @@
       "gatewayToken": "token-one",
       "ownerDisplayName": "Owner",
       "allowedSubjectIds": [
-        "ou_viewer",
+        "user_viewer",
         "example:tenant-a:user-other"
       ],
       "sessionMode": "write",

packages/experimental/liveshare-protocol/tests/frames/v1/relay-to-gateway--share-rpc.json

@@ -12,7 +12,7 @@
     "actor": {
       "providerId": "example",
       "tenantId": "tenant-a",
-      "subjectId": "ou_viewer",
+      "subjectId": "user_viewer",
       "credential": "signed-owner-verified-token"
     }
   },

packages/experimental/liveshare-protocol/tests/frames/v1/worker-to-host--share-rpc-request.json

@@ -6,7 +6,7 @@
     "id": 7,
     "shareId": "share-one",
     "body": { "op": "stream-open", "id": 1, "endpoint": "trajectory", "payload": {} },
-    "actor": { "providerId": "example", "tenantId": "tenant-a", "subjectId": "ou_viewer" }
+    "actor": { "providerId": "example", "tenantId": "tenant-a", "subjectId": "user_viewer" }
   },
   "required": ["type", "id", "shareId", "actor"],
   "optional": ["body"]