[JS] Genkit Vertex plugin not working in ESM mode

[oerhahon]

Describe the bug
node:internal/modules/esm/resolve:254
throw new ERR_UNSUPPORTED_DIR_IMPORT(path, fileURLToPath(base), String(resolved));
^

Error [ERR_UNSUPPORTED_DIR_IMPORT]: Directory import 'C:\sample\node_modules@genkit-ai\vertexai\lib\vector-search' is not supported resolving ES modules imported from C:\sample\node_modules@genkit-ai\vertexai\lib\index.mjs
at finalizeResolution (node:internal/modules/esm/resolve:254:11)
at moduleResolve (node:internal/modules/esm/resolve:921:10)
at defaultResolve (node:internal/modules/esm/resolve:1124:11)
at ModuleLoader.defaultResolve (node:internal/modules/esm/loader:557:12)
at ModuleLoader.resolve (node:internal/modules/esm/loader:526:25)
at ModuleLoader.getModuleJob (node:internal/modules/esm/loader:249:38)
at ModuleJob._link (node:internal/modules/esm/module_job:126:49) {
code: 'ERR_UNSUPPORTED_DIR_IMPORT',
url: 'file:///C:/sample/node_modules/@genkit-ai/vertexai/lib/vector-search'
}

Node.js v22.5.1

"@genkit-ai/vertexai": "^0.5.13",

To Reproduce
use genkit init, rename src/index.ts to src/index.mjs, and add "type": "module" to package