add refresh_gencode.sh script to Java smoke tests (#25671)

Closes #25671

COPYBARA_INTEGRATE_REVIEW=#25671 from protocolbuffers:salo-script 6e81bbd
PiperOrigin-RevId: 865150539

Author: ericsalo

compatibility/smoke/refresh_gencode.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/bash
+# Run this script to update the gencode for all version subdirs.
+# Answer yes when prompted about removing write-protected files.
+
+set -e -x
+
+build="BUILD.bazel"
+
+# Copy and eventually restore the original build file.
+cp "${build}" "${build}".original
+trap "mv ${build}.original ${build}" EXIT
+
+# Update the subdirs.
+for file in v*; do
+	add_gencode.sh "${file:1}"
+done