Make a soong-only copy of generate-notice-files.py

This is an unchanged copy of build/make/tools/generate-notice-files.py

After this change, the make implementation of generate-notice-files.py
will change to take a required parameter for $(PRODUCT_OUT) and will
only include notices for files built under $(PRODUCT_OUT).

Because soong has the ability to walk dependency trees, the soong
version will likely change in the future to use that ability causing
both versions to move in different directions.

After those changes are complete, we can look into factoring out any
remaining shared logic.

Test: run manually and system image notices checked for changes

Change-Id: Id139a66503457615548b46e7996349ca0817e831