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/mapmerge2/convert.py

@@ -0,0 +1,8 @@
+#!/usr/bin/env python3
+import frontend
+import dmm
+
+if __name__ == '__main__':
+    settings = frontend.read_settings()
+    for fname in frontend.process(settings, "convert"):
+        dmm.DMM.from_file(fname).to_file(fname, settings.tgm)