Add postinstall script to fix FBReactNativeSpec hash change

The hash in Podfile.lock keep changing on different developer machines. That is because the file the hash is based on contains absolute paths.
See facebook/react-native#31193 for more info.

This commit adds a postinstall script that fixes that bug.

packages/app/ios/Podfile.lock

@@ -542,7 +542,7 @@ SPEC CHECKSUMS:
   CocoaAsyncSocket: 065fd1e645c7abab64f7a6a2007a48038fdc6a99
   DoubleConversion: cf9b38bf0b2d048436d9a82ad2abe1404f11e7de
   FBLazyVector: 49cbe4b43e445b06bf29199b6ad2057649e4c8f5
-  FBReactNativeSpec: 0b41cf9e0b74ffa97ededb3d0210da5b4710474c
+  FBReactNativeSpec: 5e508b58518de4f083a88fb46f48d79c62fdc988
   Flipper: d3da1aa199aad94455ae725e9f3aa43f3ec17021
   Flipper-DoubleConversion: 38631e41ef4f9b12861c67d17cb5518d06badc41
   Flipper-Folly: f7a3caafbd74bda4827954fd7a6e000e36355489

packages/app/package.json

@@ -12,7 +12,8 @@
     "test:watch": "jest --watch",
     "typecheck": "tsc --watch",
     "i18n": "sync-i18n --files '**/translations/*.json' --primary en --languages ar de pl so sv --space 2",
-    "check-i18n": "npm run i18n -- --check"
+    "check-i18n": "npm run i18n -- --check",
+    "postinstall": "./postinstall-fix-rn-064-bugs.sh"
   },
   "dependencies": {
     "@eva-design/eva": "2.0.0",

packages/app/postinstall-fix-rn-064-bugs.sh

@@ -0,0 +1,26 @@
+#!/bin/bash
+
+OS=`uname`
+
+echo "Fixing RN 0.64.0 bugs:"
+cd node_modules/react-native/scripts
+echo "- unset PREFIX in find-node.sh"
+if [ `cat find-node.sh | grep 'unset PREFIX' | wc -l` -lt 1 ]
+then
+  cp find-node.sh tmp
+  head -n 1 tmp >find-node.sh
+  echo "unset PREFIX" >>find-node.sh
+  tail -n +2 tmp >>find-node.sh
+  rm tmp
+fi
+
+if [ "$OS" = 'Darwin' ]
+then
+  # for MacOS; cannot install Pods on Win/Linux
+  echo "- switch to relative paths in react_native_pods.rb "
+  sed -i '' -e "s/File[.]join[(]__dir__, \"[.][.]\"[)]/\"..\/..\/node_modules\/react-native\"/" react_native_pods.rb
+  sed -i '' -e "s/#{File[.]join[(]__dir__, \"generate-specs.sh\"[)]}/..\/..\/node_modules\/react-native\/scripts\/generate-specs.sh/" react_native_pods.rb
+  sed -i '' -e "s/spec[.]prepare_command = \"#/spec.prepare_command = \"cd ..\/.. \&\& #/" react_native_pods.rb
+fi
+
+cd - >/dev/null