Use the new cached method fromJSON from google-gax

Author: mkruskal-google

templates/cjs/typescript_gapic/src/$version/$service_client.ts.njk

@@ -322,7 +322,7 @@ export class {{ service.name }}Client {
       protoFilesRoot) as (typeof protoFilesRoot);
 {%- else %}
 
-    const protoFilesRoot = this._gaxModule.protobuf.Root.fromJSON(jsonProtos);
+    const protoFilesRoot = this._gaxModule.protobufFromJSON(jsonProtos);
 {%- endif %}
 {%- endif %}
 {%- if service.longRunning.length > 0 or service.LongRunningOperationsMixin > 0%}

templates/esm/typescript_gapic/esm/src/$version/$service_client.ts.njk

@@ -332,7 +332,7 @@ export class {{ service.name }}Client {
       protoFilesRoot) as (typeof protoFilesRoot);
 {%- else %}
 
-    const protoFilesRoot = this._gaxModule.protobuf.Root.fromJSON(jsonProtos as gax.protobuf.INamespace);
+    const protoFilesRoot = this._gaxModule.protobufFromJSON(jsonProtos);
 {%- endif %}
 {%- endif %}
 {%- if service.longRunning.length > 0 or service.LongRunningOperationsMixin > 0%}