Skip analysis of non-solution files

Some exercises consist of more than one file in the `src/main/java` folder, and some of them are designed to be read-only files. These are marked as such in the exercise's `.meta/config.json` file, because they should be listed in the `files.editor` list.

For example, the [configuration for the `wizards-and-warriors-2` exercise](https://github.com/exercism/java/blob/main/exercises/concept/wizards-and-warriors-2/.meta/config.json) lists the following files as read-only:

- `src/main/java/Character.java`
- `src/main/java/Destination.java`
- `src/main/java/TravelMethod.java`

The goal of this issue is to make sure that read-only files are never processed by the analyzer.

In most cases processing these files may not introduce any issues, but just in case one of them contains code that triggers an analyzer comment we should skip them by default. If not, a student may receive feedback on a file that they did not write and cannot edit, which is just confusing.

Start with exercises/concept/wizards-and-warriors-2/.meta/config.json and trace how the analyzer reads its files.editor list. Done means files marked read-only there are excluded from analysis, while editable solution files continue to be processed.

Written by the indexing model from the issue text.