Merge RuneLite dev branches iteratively

In some cases, the merge tool cannot resolve conflicts from multiple
branches at once, leading to the script failing repeatedly regardless of
saved merge conflict resolution, etc. Instead, merging the branches one
by one ensures conflicts can be resolved properly and reduces the
complexity of conflict resolution when multiple conflicts may exist.

src/.bin/open-runelite.sh

@@ -52,7 +52,9 @@ function build_client {
 	# Update local dev branch and build
 	git checkout dev || git checkout -b dev
 	git reset --hard "$UPSTREAM_REMOTE/$UPSTREAM_BRANCH"
-	git merge --no-gpg-sign --no-edit "${BRANCHES_TO_MERGE[@]}" || exit 1
+	for branch in "${BRANCHES_TO_MERGE[@]}"; do
+		git merge --no-gpg-sign --no-edit --rerere-autoupdate "$branch" || ( [[ -z "$(git rerere diff)" ]] && git commit --no-gpg-sign --no-edit) || exit 1
+	done
 	mvn clean package -DskipTests -U || exit 1
 	git checkout -
 	# copy shaded jar to script's directory, removing any old shaded jars