AbsentOrWrongFileLicense is a bit strange. It is a rule that needs a FileProcessListener to work. The reason for it is how the rule is configured. The configuration is not inside the yaml file. In the yaml file the user writes a path and we check that the files had the same header as the content of the file in that path.

The problem: the path needs to be relative (otherwise it wouldn't work on any computer). But relative to what? The rule doesn't know the "base" path to resolve that relative path. For that reason the implementation was using a FileProcessListener. There we can check the absolute path of the config files (yamls). FileProcessListener takes the absolute path of the last yaml as the base path and the resolves the file location. That "last" yaml is also a bit strange. In general it works but it could generate problems.

What this PR does is to remove that complexity away. Instead of using a relative path the user provides us with the header inside the yaml so all those problems go away. yaml has a multiple ways to write multiline strings. For example:

comments:
  AbsentOrWrongFileLicense:
    licenseTemplate: |
      /* Your lincense
       * Here
       */
    licenseTemplate: false

Context:

The initial reason for this change was to unblock: #8681 because to test the interaction between the FileProcessListener and the Rule it was using some functions provided by core through detekt-test. But I found another way to fix that problem. But when I realized this PR was ready to publish and I think that it is still beneficial.