exec macos app for better output when using bazel run (bazelbuild#2019)

Author: dmaclach

apple/internal/templates/macos.template.sh

@@ -39,4 +39,4 @@ readonly BUNDLE_INFO_PLIST="${APP_DIR}/Contents/Info.plist"
 readonly BUNDLE_EXECUTABLE=$(/usr/libexec/PlistBuddy -c "Print :CFBundleExecutable" "${BUNDLE_INFO_PLIST}")
 
 # Launch the app binary
-"${APP_DIR}/Contents/MacOS/${BUNDLE_EXECUTABLE}" "$@"
+exec "${APP_DIR}/Contents/MacOS/${BUNDLE_EXECUTABLE}" "$@"