Fix S1104 FP: Do not report in Unity serializable classes

[sebastien-marichal]

Fixes #7522

Ignore fields in the following Unity classes:

• ScriptableObject
• MonoBehaviour

[mary-georgiou-sonarsource]

My understanding from the docs is that you should include UnityEngine.Object.
Which, if I'm not wrong, is parent to UnityEngine_ScriptableObject so you can replace one with the other.

But for custom classes which don’t derive from UnityEngine.Object, Unity includes the state of the instance directly in the serialized data of the MonoBehaviour or ScriptableObject that references them. There are two ways that this can happen: inline and by [SerializeReference]
.```

[sebastien-marichal]

Adding UnityEngine.Object is not enough, the class should also have the Serializable attribute.
I can add it so it also supports custom serializable unity class/object.
I will rework a bit the logic then.

[sebastien-marichal]

After a closer look, the required attribute for custom objects is System.Serializable, and this is already an exception to the rule.

Edit 1: Never mind, I didn't realize we were only checking if the field had the attribute. I have pushed my updates.

Edit 2: I am having strokes, we do check if the parent class has the Serializable field. In any case, I have added more UTs to check for custom Unity serializable classes.

[mary-georgiou-sonarsource]

Looks good - one minor change.

[sonarcloud]

Quality Gate passed for 'Sonar .NET Java Plugin'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[sonarcloud]

Quality Gate passed for 'SonarAnalyzer for .NET'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[mary-georgiou-sonarsource]

LGTM!