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.bat

@@ -0,0 +1,14 @@
+@echo off
+cd %~dp0
+for %%f in (*.hook) do (
+	echo Installing hook: %%~nf
+	copy %%f ..\..\.git\hooks\%%~nf >nul
+)
+for %%f in (*.merge) do (
+	echo Installing merge driver: %%~nf
+	echo [merge "%%~nf"]^
+
+	driver = tools/hooks/%%f %%P %%O %%A %%B %%L >> ..\..\.git\config
+)
+echo Done
+pause

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"

tools/hooks/pre-commit.hook

@@ -0,0 +1,2 @@
+#!/bin/bash
+exec tools/hooks/python.sh -m precommit

tools/hooks/python.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+set -e
+if command -v python3 >/dev/null 2>&1; then
+	PY=python3
+else
+	PY=python
+fi
+PATHSEP=$($PY - <<'EOF'
+import sys, os
+if sys.version_info.major != 3 or sys.version_info.minor < 6:
+	sys.stderr.write("Python 3.6+ is required: " + sys.version + "\n")
+	exit(1)
+print(os.pathsep)
+EOF
+)
+export PYTHONPATH=tools/mapmerge2/${PATHSEP}${PYTHONPATH}
+$PY "$@"