Add a new and improved mapmerge (#33869)

Key benefits of the new mapmerge include: multi-Z support, effective
reuse of deleted keys, automatic handling of key overflow, and utilizing
a git pre-commit hook to eliminate the need to run batch files manually.

tools/hooks/install.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+cd "$(dirname "$0")"
+for f in *.hook; do
+	echo Installing hook: ${f%.hook}
+	cp $f ../../.git/hooks/${f%.hook}
+done
+for f in *.merge; do
+	echo Installing merge driver: ${f%.merge}
+	git config --replace-all merge.${f%.merge}.driver "tools/hooks/$f %P %O %A %B %L"
+done
+echo "Done"