fix(build): share one ESM module graph across the root, /server and /3d entries

[rpinckne]

Problem

rollup.config.mjs builds each entry on its own, so dist/3d/index.modern.mjs carries its own copy of every module it shares with the root, React contexts included. A Map3D imported from @vis.gl/react-google-maps/3d therefore reads a different APIProviderContext than the APIProvider imported from @vis.gl/react-google-maps, and throws:

<Map3D> can only be used inside an <APIProvider> component.

That pairing is exactly what the 1.10.0 deprecation notices and examples/map-3d point people at (the example imports APIProvider from the root and Map3D from /3d). The root Pin likewise cannot see a /3d Marker3D, because it reads the root Marker3DContext.

Reproduction against the published 1.10.0 package:

import React from 'react'
import { renderToString } from 'react-dom/server'
import * as root from '@vis.gl/react-google-maps'
import * as threeD from '@vis.gl/react-google-maps/3d'

root.GoogleMaps3DContext === threeD.GoogleMaps3DContext // false
renderToString(React.createElement(root.APIProvider, { apiKey: 'x' },
  React.createElement(threeD.Map3D, { mode: 'SATELLITE' }))) // throws

Change

The ESM output becomes one code-split build over all three entries (index, server/index, 3d/index): shared modules are emitted once under dist/chunks/ and every entry imports the same instance. UMD cannot code-split, so those builds stay self-contained, and the per-entry .d.ts builds are unchanged. package.json#files already whitelists dist, so the chunks ship.

Built layout:

dist/index.modern.mjs          → ./chunks/popover-*.mjs, ./chunks/static-map-*.mjs
dist/3d/index.modern.mjs       → ../chunks/popover-*.mjs
dist/server/index.modern.mjs   → ../chunks/static-map-*.mjs
dist/{index,3d/index,server/index}.{umd.js,d.ts}   (as before)

Verification

Same script as above against the build from this branch: GoogleMaps3DContext, Marker3DContext, Map3D, Marker3D, and Popover are identical objects across the two entries, and the root APIProvider + /3d Map3D render. npm test passes (23 suites), npm run build produces the layout above.

An app that imports both entries now also loads the shared code once instead of twice.