fix: allow bare imports of ts packages in a monorepo

[sheremet-va]

Description

This PR adds support for bare imports of packages that export a TS entry point:

import pkg from '@monorepo/ts' // <-- exports .ts file
export default defineConfig({
  ...pkg.sharedConfig,
})

Currently, vite resolves the .ts file but keeps it external which breaks in Node:

TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts" for /react-monorepo-ts/packages/components/src/test.ts

TODO

• Tests

[bluwy]

fwiw this looks similar to #17323

[sheremet-va]

Superseded by #18637