* Check dependencies' open-source licenses
Use jk1/Gradle-License-Report to verify that all
dependencies have open-source licenses.
Note that the following dependencies are not checked:
Dependencies of official Gradle plugins
Dependencies declared in buildscript block
Dependencies of jk1/Gradle-License-Report itself
* Refactor the license check to be a generic presubmit check
This includes all of the old presubmits that were in our METADATA file
that are still valid.
* Responses to CR
Added docstrings, refactored the file finder, changed variable names,
and formatted the file
* More respones to CR
The check for environment cannot be done when the task is defined,
otherwise running any task will fail when the check does not pass.
Instead, check the environment when the task executes.
