Support entry file name build output other than `${entryName}.js`

[hi-ogawa]

Currently preview server and import.meta.viteRsc.loadModule excepts exact file name e.g. index.js, but this is not the case when customizing entry file names.

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

Lines 535 to 538 in d1627cb

	const entryFile = path.join(
	manager.config.environments[options.environmentName]!.build.outDir,
	`${options.entryName}.js`,
	)

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

Lines 752 to 756 in d1627cb

	path.join(
	config.environments[toEnv!]!.build.outDir,
	// TODO: this breaks when custom entyFileNames
	`${entryName}.js`,
	),