fix(esm-shim): match typings to actual exports

[mahirhir]

The hand-written types/index.d.ts for @rollup/plugin-esm-shim does not match what the package actually exports.

src/index.ts exposes the plugin as both a named and a default export, and re-exports the Output type:

export * from './types';   // Output
export default esmShim;
export { esmShim };

The typings only declare the default, under the stale name commonjsShim, and omit the named esmShim export. As a result import { esmShim } from '@rollup/plugin-esm-shim' does not type-check even though it works at runtime.

This is the same typings/exports drift that #1985 fixed for @rollup/plugin-swc. Every other plugin with a named export already declares it in its typings (swc, babel, wasm, node-resolve, html, dynamic-import-vars); esm-shim is the one that was left out.

Changes:

• declare the named esmShim export and give the default its real name, matching the shape fix(swc): fix typings to match actual exports #1985 landed (export function swc(...): Plugin; export default swc;)
• export the Output type, which src/index.ts already re-exports from ./types
• assert the named export in the package's existing test:ts type test

pnpm --filter @rollup/plugin-esm-shim test:ts reports has no exported member 'esmShim' on the current typings and passes with this change.

[mahirhir]

Closing this myself: the repository has had no push in 99 days, so there is no one to review it right now. No hard feelings and no action needed. If the project picks up again and this is still wanted, I am happy to reopen or re-send it.