goworksync: include running go mod tidy

Find all the 'go.mod' files in the repository, then change to it's
directory and run 'go mod tidy'.  This helps us ensure that all deps
information are within the go.mod files and thus help 'go work sync'
work properly.

tools/goworksync.sh

@@ -3,6 +3,17 @@
 GOBIN=$1
 
 (
-    cd $BUILD_WORKSPACE_DIRECTORY
-    $(bazel info execution_root)/$GOBIN work sync
+	cd "$BUILD_WORKSPACE_DIRECTORY" || exit
+	GO="$(bazel info execution_root)/$GOBIN"
+
+	find . -name go.mod |
+		while IFS= read -r -d '' f; do
+			d=$(dirname "$f")
+			(
+				cd "$d" || exit
+				"$GO" mod tidy
+			)
+		done
+
+	"$GO" work sync
 )