Third-party licenses files are located inside the `third_party` folders.

Closes #37920
https://github.com/dart-lang/sdk/pull/37920

GitOrigin-RevId: 0baec7bcb079bf56658e29cbdab83149ec211d6b
Change-Id: I8a1e6fcb682d961f6390272e7bb5eadd5ff1dcf6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/113842


Reviewed-by: Michael Thomsen <mit@google.com>