Add LICENSE file check in common tools

Everyone should be using the license file content from https://docs.opensource.microsoft.com/releasing/maintain/license/ and for consistency we should use the file name LICENSE and not LICENSE.txt. We should always have a LICENSE file in the root of the repo and we should also include one with the package if that is the way the ecosystem works. For example, python, go and js are source-based packages so in those cases we also need to have a copy of the file in each package folder in the repo. For Nuget the recommendation is to set the license via the package metadata and not have the file copied all over the repo. So if we can avoid having the file duplicated for every package in the repo we should be we cannot in all cases.

We should create a pipeline check to ensure that the license file matches in content as well as file name so we can plug it into our various language pipelines.