perf(backend): parse5をやめて軽量な実装にし、メモリ削減・高速化 (#16892)

* wip

* test

* Revert "test"

This reverts commit b7c5ae7214.

* Update MfmService.ts

packages/backend/src/server/oauth/OAuth2ProviderService.ts

@@ -120,7 +120,7 @@ async function discoverClientInformation(logger: Logger, httpRequestService: Htt
 		}
 
 		const text = await res.text();
-		const fragment = htmlParser.parse(text);
+		const fragment = htmlParser.parse(`<div>${text}</div>`);
 
 		redirectUris.push(...[...fragment.querySelectorAll('link[rel=redirect_uri][href]')].map(el => el.attributes.href));