Add MPL support to add3prf.py

This adds the ability to detect and generate the correct METADATA file
for MPL licensed crates.

Bug: 308477037
Test: atest --host add3prf_test; Ran against https://crates.io/crates/fdt
Change-Id: I2b1765a08b68c5eb59e4f52b33c1df337e8c148b
2 files changed