Revert "feat: improve monorepo support by removing redundant PROJECT_ROOT (facebook#28354)"

This reverts commit a8e8502.

Author: grabbou

scripts/react-native-xcode.sh

@@ -56,17 +56,11 @@ case "$CONFIGURATION" in
     ;;
 esac
 
-# Setting up a project root was a workaround to enable support for non-standard
-# structures, including monorepos. Today, CLI supports that out of the box
-# and setting custom `PROJECT_ROOT` only makes it confusing. 
-#
-# As a backwards-compatible change, I am leaving "PROJECT_ROOT" support for those
-# who already use it - it is likely a non-breaking removal.
-#
-# For new users, we default to $PWD - not changing things all.
-#
-# For context: https://github.com/facebook/react-native/commit/9ccde378b6e6379df61f9d968be6346ca6be7ead#commitcomment-37914902
-PROJECT_ROOT=${PROJECT_ROOT:-$PWD}
+# Path to react-native folder inside node_modules
+REACT_NATIVE_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+# The project should be located next to where react-native is installed
+# in node_modules.
+PROJECT_ROOT=${PROJECT_ROOT:-"$REACT_NATIVE_DIR/../.."}
 
 cd "$PROJECT_ROOT" || exit
 
@@ -109,9 +103,6 @@ if [[ ! -x node && -d ${HOME}/.anyenv/bin ]]; then
   fi
 fi
 
-# Path to react-native folder inside node_modules
-REACT_NATIVE_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
-
 # check and assign NODE_BINARY env
 # shellcheck source=/dev/null
 source "$REACT_NATIVE_DIR/scripts/node-binary.sh"