Refactor XContentType to mediaType (opensearch-project#721)

Signed-off-by: Hailong Cui <[email protected]>
(cherry picked from commit d0a322c)

notifications/notifications/src/test/kotlin/org/opensearch/integtest/PluginRestTestCase.kt

@@ -17,12 +17,12 @@ import org.opensearch.client.RestClient
 import org.opensearch.client.WarningsHandler
 import org.opensearch.common.io.PathUtils
 import org.opensearch.common.settings.Settings
-import org.opensearch.common.xcontent.XContentType
 import org.opensearch.commons.ConfigConstants
 import org.opensearch.commons.notifications.model.ConfigType
 import org.opensearch.commons.rest.SecureRestClientBuilder
 import org.opensearch.core.rest.RestStatus
 import org.opensearch.core.xcontent.DeprecationHandler
+import org.opensearch.core.xcontent.MediaType
 import org.opensearch.core.xcontent.NamedXContentRegistry
 import org.opensearch.notifications.NotificationPlugin
 import org.opensearch.rest.RestRequest
@@ -67,7 +67,7 @@ abstract class PluginRestTestCase : OpenSearchRestTestCase() {
 
         val pluginIndices = listOf(".opensearch-notifications-config")
         val response = client().performRequest(Request("GET", "/_cat/indices?format=json&expand_wildcards=all"))
-        val xContentType = XContentType.fromMediaType(response.entity.contentType.value)
+        val xContentType = MediaType.fromMediaType(response.entity.contentType.value)
         xContentType.xContent().createParser(
             NamedXContentRegistry.EMPTY,
             DeprecationHandler.THROW_UNSUPPORTED_OPERATION,