refactor: Use ESM (#8358)

* wip

* wip

* fix

* clean up

* Update tsconfig.json

* Update activitypub.ts

* wip

packages/backend/test/loader.js

@@ -0,0 +1,37 @@
+import path from 'path'
+import typescript from 'typescript'
+import { createMatchPath } from 'tsconfig-paths'
+import { resolve as BaseResolve, getFormat, transformSource } from 'ts-node/esm'
+
+const { readConfigFile, parseJsonConfigFileContent, sys } = typescript
+
+const __dirname = path.dirname(new URL(import.meta.url).pathname)
+
+const configFile = readConfigFile('./test/tsconfig.json', sys.readFile)
+if (typeof configFile.error !== 'undefined') {
+  throw new Error(`Failed to load tsconfig: ${configFile.error}`)
+}
+
+const { options } = parseJsonConfigFileContent(
+  configFile.config,
+  {
+    fileExists: sys.fileExists,
+    readFile: sys.readFile,
+    readDirectory: sys.readDirectory,
+    useCaseSensitiveFileNames: true,
+  },
+  __dirname
+)
+
+export { getFormat, transformSource }  // こいつらはそのまま使ってほしいので re-export する
+
+const matchPath = createMatchPath(options.baseUrl, options.paths)
+
+export async function resolve(specifier, context, defaultResolve) {
+  const matchedSpecifier = matchPath(specifier.replace('.js', '.ts'))
+  return BaseResolve(  // ts-node/esm の resolve に tsconfig-paths で解決したパスを渡す
+    matchedSpecifier ? `${matchedSpecifier}.ts` : specifier,
+    context,
+    defaultResolve
+  )
+}