Support vendoring Hermes for out-of-tree platforms

[shirakaba]

Currently, we look up the appropriate version of hermes from react-native like so:

react-native-node-api/packages/host/src/node/cli/hermes.ts

Lines 31 to 38 in 0419678

	const appPackageRoot = packageDirectorySync({ cwd: from });
	assert(appPackageRoot, "Failed to find package root");
	const reactNativePath = path.dirname(
	require.resolve("react-native/package.json", {
	// Ensures we'll be patching the React Native package actually used by the app
	paths: [appPackageRoot],
	}),
	);

For out-of-tree platforms like react-native-macos, though, I had to apply the following patch before it'd resolve the correct root during pod install:

let reactNativePath;
if(from.endsWith("ios") || from.endsWith("android")){
  reactNativePath = node_path_1.default.dirname(require.resolve("react-native/package.json", {
      // Ensures we'll be patching the React Native package actually used by the app
      paths: [appPackageRoot],
  }));
} else if(from.endsWith("macos")){
  reactNativePath = node_path_1.default.dirname(require.resolve("react-native-macos/package.json", {
      // Ensures we'll be patching the React Native package actually used by the app
      paths: [appPackageRoot],
  }));
} else if(from.endsWith("windows")){
  reactNativePath = node_path_1.default.dirname(require.resolve("react-native-windows/package.json", {
      // Ensures we'll be patching the React Native package actually used by the app
      paths: [appPackageRoot],
  }));
} else {
  throw new Error("Unsupported platform.");
}

There is surely a more elegant way to do it (it would be nicest to know the platform for certain, rather than just guessing based on the presence of an ios/android/macos folder in the path), but just to illustrate the point.

[kraenhansen]

Another issue here is that we download the Hermes fork into the host package (node_modules/react-native-node-api/hermes) and assume there will be a single version needed. Perhaps we should download it into the react-native package (or react-native-macos / react-native-windows) instead? 🤔

I've put up a #287 as a suggestion - let me know what you think 🙂

[kraenhansen]

Reopening the issue, since we'd like to detect the relevant --react-native-package, either in scripts/patch-hermes.rb or as part of computing a default value inside the CLI.