Stop publishing jest/preprocessor.js to npm

Summary:
Changelog:
[Breaking][General] Remove jest/preprocessor from the react-native package

Using `react-native/jest/preprocessor` outside of the React Native repo has been deprecated since D34820086 (facebook@c1e9aa9). Here, we make this file private and stop publishing it to npm.

The supported method of using Jest in React Native projects is using the [Jest preset](https://jestjs.io/docs/tutorial-react-native) shipped as part of the `react-native` package.

NOTE: We could probably make some of the other files under `jest/` private as well, but we should go through a separate deprecation cycle with those, in case they are also being used externally by some projects. I'm leaving that for future followup at the moment.

Reviewed By: GijsWeterings

Differential Revision: D36132939

fbshipit-source-id: 300ffa6cf16232573cd3a79a34c14daaafd7aa43

Author: motiz88

jest.config.js

@@ -13,7 +13,7 @@ module.exports = {
   transform: {
     '^.+\\.(bmp|gif|jpg|jpeg|mp4|png|psd|svg|webp)$':
       '<rootDir>/jest/assetFileTransformer.js',
-    '.*': './jest/preprocessor_DO_NOT_USE.js',
+    '.*': './jest/private/preprocessor.js',
   },
   setupFiles: ['./jest/setup.js'],
   timers: 'fake',

jest/preprocessor.js

@@ -14,9 +14,6 @@
     "outputName": "js-test-results.xml"
   },
   "files": [
-    "!template/node_modules",
-    "!template/package-lock.json",
-    "!template/yarn.lock",
     "android",
     "cli.js",
     "flow",
@@ -25,6 +22,7 @@
     "interface.js",
     "jest-preset.js",
     "jest",
+    "!jest/private",
     "Libraries",
     "LICENSE",
     "local-cli",
@@ -60,6 +58,9 @@
     "sdks/hermes-engine.podspec",
     "template.config.js",
     "template",
+    "!template/node_modules",
+    "!template/package-lock.json",
+    "!template/yarn.lock",
     "third-party-podspecs"
   ],
   "scripts": {