scripts: restore utils/migrate_includes.py

Commit 9b30667c
("build: drop LEGACY_INCLUDE_PATH support")
removed scripts/utils/migrate_includes.py.

This was premature. This script is still useful to users of older
versions of zephyr that are attempting to migrate to current ones.

For example, users of v2.7 LTS who are migrating to v3.4 should
still be able to run the script to migrate their code bases.

Restore it. Maybe after next LTS we can remove it. It costs
basically nothing to keep it in the tree.

Signed-off-by: Martí Bolívar <mbolivar@amperecomputing.com>