Flag sources with incompatible licenses (e.g. Google Maps)

[quincylvania]

We currently flag changeset comments that mention Google:

We should create an "Incompatible Data Source" validation warning that similarly flags source tags with such text on features.

Edit: This comment previously mentioned turning the changeset warning into a native validation issue. This would involve validating the actual changeset, which the validator isn't set up to do right now. We could consider this later in a separate issue if we really want to.