Better handling of enum comparisons

### What

Comparing enums with `<`, `>`, `=`, `!=` is not ideal, because adding new entries to the enum could break the original assumptions.

*Originally suggested at https://github.com/eclipse-score/lifecycle/pull/392#discussion_r3691420273*

### Acceptance Criteria (DoD)

- No comparisons using `<` or `>`
- Minimal comparisons using `=` or `!=`

### How

In most cases, a `switch` without a `default` is much more robust.

For example:

```cpp
FileExistenceState convertFileExistenceState(fb::FileExistenceState fb_state)
{
switch (fb_state)
{
case fb::FileExistenceState::Deleted:
return FileExistenceState::Deleted;
case fb::FileExistenceState::Exists:
return FileExistenceState::Exists;
}

SCORE_LANGUAGE_FUTURECPP_UNREACHABLE_MESSAGE("Invalid fb::FileExistenceState");
}
```

Not having a `default` triggers a compiler warning when a new entry is added to the enum, prompting the developer to consider the desired behaviour and add a new `case`.

Because it is possible (using casts) to create a value which does not correspond to any enum entry, `SCORE_LANGUAGE_FUTURECPP_UNREACHABLE` is needed to satisfy the compiler that the function will return in all cases. This will crash the program if an invalid value is seen.