Define "react-native-strict-api" type exports (#50909)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/50909

Enables and maps the `types_generated/` directory for `react-native` and `react-native/virtualized-lists` — exposing the new Strict TypeScript API entry points to React Native.

**New `"exports"` conditions**

- `"react-native-strict-api"` — The Strict TypeScript API opt in, exposing the `index.d.ts` entry point only.
- `"react-native-strict-api-UNSAFE-ALLOW-SUBPATHS"` — Opts into the new from-source generated types, but allows accessing subpaths (unsafe).
    - We intend for this unsafe condition to be an escape hatch for Frameworks only (i.e. Expo).

Note: In the case of `virtualized-lists`, we simply use the `"types"` condition — since this package did not expose any TypeScript API previously.

NOTE: Should we need to roll back JS Stable API phase 1, **this is the single diff to revert**.

Changelog:
[General][Added] - Configure the "react-native-strict-api" opt in for our next-gen TypeScript API

Reviewed By: cipolleschi

Differential Revision: D71969602

fbshipit-source-id: 291182cc826db8b33f21fc79698e6096876d17ef

packages/react-native/package.json

@@ -29,11 +29,28 @@
   "main": "./index.js",
   "types": "types",
   "exports": {
-    ".": "./index.js",
-    "./*": "./*.js",
-    "./*.js": "./*.js",
-    "./Libraries/*.d.ts": "./Libraries/*.d.ts",
-    "./types/*.d.ts": "./types/*.d.ts",
+    ".": {
+      "react-native-strict-api": "./types_generated/index.d.ts",
+      "react-native-strict-api-UNSAFE-ALLOW-SUBPATHS": "./types_generated/index.d.ts",
+      "default": "./index.js"
+    },
+    "./*": {
+      "react-native-strict-api": null,
+      "react-native-strict-api-UNSAFE-ALLOW-SUBPATHS": "./types_generated/*.d.ts",
+      "default": "./*.js"
+    },
+    "./*.js": {
+      "react-native-strict-api": null,
+      "default": "./*.js"
+    },
+    "./Libraries/*.d.ts": {
+      "react-native-strict-api": null,
+      "default": "./Libraries/*.d.ts"
+    },
+    "./types/*.d.ts": {
+      "react-native-strict-api": null,
+      "default": "./types/*.d.ts"
+    },
     "./gradle/*": null,
     "./React/*": null,
     "./ReactAndroid/*": null,
@@ -110,6 +127,7 @@
     "!src/private/testing",
     "third-party-podspecs",
     "types",
+    "types_generated",
     "!**/__docs__/**",
     "!**/__fixtures__/**",
     "!**/__flowtests__/**",

packages/virtualized-lists/package.json

@@ -19,11 +19,23 @@
   "engines": {
     "node": ">=18"
   },
+  "exports": {
+    ".": {
+      "types": "./types_generated/index.d.ts",
+      "default": "./index.js"
+    },
+    "./*": {
+      "types": null,
+      "default": "./*.js"
+    },
+    "./package.json": "./package.json"
+  },
   "files": [
     "index.js",
     "index.d.ts",
     "Lists",
     "README.md",
+    "types_generated",
     "Utilities",
     "!**/__docs__/**",
     "!**/__fixtures__/**",