This generates a `license.md` file with all the relevant information about
the different libraries and their respecive licenses.
This should replace: THIRD-PARTY-LICENSES.txt
Important files:
* `make_license.py` (main script called by `make license`.
* `licenses.json` (file to add the definition of new licenses).
* `licenses/*/*.txt` (individual license files.
The `license.md` groups the libraries per license, list their
corresponding copyright information and include the complete license.
Code includes contributions from:
* Campbell Barton (multi-line parser for versions.cmake).
* Thomas Dinges (Windows support for `make license`).
Part of: !129018
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