fix: Access to relative paths when invoking test-manual-e2e (facebook#33000)

Summary:
Running `test-manual-e2e.sh` from any folder other than the repo root results in errors regarding files not existing, that's because we're not taking into consideration the path from where the script is invoked. This PR updates it so that we get the absolute path of the script and then use it to get the parent directory and `cd` to the repo root folder.

Closes facebook#32999

## Changelog

[Internal] [Fixed] - fix access to relative paths when invoking `test-manual-e2e.sh` from folders other than the repo root

Pull Request resolved: facebook#33000

Test Plan:
1. Clone this repo
2. Navigate to the rn-tester folder `cd packages/rn-tester/`
3. Run `../../scripts/test-manual-e2e.sh`
4. Select RNTester, Android and Hermes

https://user-images.githubusercontent.com/11707729/151730441-18bc37de-0224-4f5e-a2fe-408e3ace5c1f.mov

Reviewed By: ShikaSD

Differential Revision: D33915561

Pulled By: cortinico

fbshipit-source-id: 66f2d1ebee50bba3fe884d6346ea08ffced47a96

Author: gabrieldonadel

scripts/test-manual-e2e.sh

@@ -11,6 +11,7 @@ ENDCOLOR="\033[0m"
 
 error() {
     echo -e "$RED""$*""$ENDCOLOR"
+    popd >/dev/null || exit
     exit 1
 }
 
@@ -22,6 +23,10 @@ info() {
     echo -e "$BLUE""$*""$ENDCOLOR"
 }
 
+# Ensures commands are executed from the repo root folder
+dir_absolute_path=$( cd "$(dirname "${BASH_SOURCE[0]}")" || exit ; pwd -P )
+pushd "$dir_absolute_path/../" >/dev/null || exit
+
 repo_root=$(pwd)
 selected_platform=""
 selected_vm=""
@@ -126,7 +131,7 @@ init_template_app(){
 
     project_name="RNTestProject"
 
-    cd /tmp/ || exit
+    pushd /tmp/ >/dev/null || exit
     rm -rf "$project_name"
     node "$repo_root/cli.js" init "$project_name" --template "$repo_root"
 
@@ -135,13 +140,15 @@ init_template_app(){
     grep -E "com.facebook.react:react-native:\\+" "${project_name}/android/app/build.gradle" || error "Dependency in /tmp/${project_name}/android/app/build.gradle must be com.facebook.react:react-native:+"
 
     success "New sample project generated at /tmp/${project_name}"
+    popd >/dev/null || exit
 }
 
 test_template_app(){
     if [ "$PACKAGE_VERSION" == "" ]; then
         init_template_app
     fi
 
+    pushd "/tmp/${project_name}" >/dev/null || exit
     if [ "$selected_platform" == "1" ]; then
         info "Test the following on Android:"
         info "   - Disable Fast Refresh. It might be enabled from last time (the setting is stored on the device)"
@@ -150,7 +157,7 @@ test_template_app(){
         info "Press any key to run the sample in Android emulator/device"
         info ""
         read -r -n 1
-        cd "/tmp/${project_name}" && npx react-native run-android
+        npx react-native run-android
     elif [ "$selected_platform" == "2" ]; then
         info "Test the following on iOS:"
         info "   - Disable Fast Refresh. It might be enabled from last time (the setting is stored on the device)"
@@ -163,9 +170,9 @@ test_template_app(){
         info "Press any key to open the project in Xcode"
         info ""
         read -r -n 1
-        open "/tmp/${project_name}/ios/${project_name}.xcworkspace"
+        open "ios/${project_name}.xcworkspace"
     fi
-    cd "$repo_root" || exit
+    popd >/dev/null || exit
 }
 
 
@@ -209,6 +216,7 @@ handle_menu_input(){
     if [ "$confirm" == "${confirm#[Yy]}" ]; then
         info "Next steps:"
         info "https://github.com/facebook/react-native/wiki/Release-Process"
+        popd >/dev/null || exit
         exit 1
     else
         show_menu