Support merging client reference chunks

[hi-ogawa]

See contexts in hi-ogawa/vite-plugins#895 hi-ogawa/vite-plugins#904. We probably need to set preserveEntrySignatures: "allow-extension" somewhere https://rollupjs.org/configuration-options/#preserveentrysignatures

[hi-ogawa]

Instead of relying on emitFile + manualChunks, it might be easier to expose own API to let users control this virtual construction

vite-plugin-react/packages/plugin-rsc/src/plugin.ts

Lines 1115 to 1129 in 6924db4

	for (const meta of Object.values(manager.clientReferenceMetaMap)) {
	// vite/rollup can apply tree-shaking to dynamic import of this form
	const key = JSON.stringify(meta.referenceKey)
	const id = JSON.stringify(meta.importId)
	const exports = meta.renderedExports
	.map((name) => (name === 'default' ? 'default: _default' : name))
	.sort()
	code += `
	${key}: async () => {
	const {${exports}} = await import(${id});
	return {${exports}};
	},
	`
	}
	code = `export default {${code}};\n`

To be able to group import(id), we'll probably need another wrapper virtual for each group though, which will then maybe start to look like hi-ogawa/vite-plugins#891