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
Change the license detection logic to return if a dual-license was
found. Update the metadata comment as discussed in b/179902335.
Add unit tests for add_module_license and decide_license_type.
Bug: 179902335
Test: atest --host add3prf_test; manually run add3prf.py in {ahash,
libloading, parking_lot, ring}
Change-Id: I3184b5cf0955d124170b9e5987308507bdef6e9a