Currently, we’re using scalar values to trace paths. The problem with
that approach is that we can’t create a reliable hierarchy with them, as
we can’t know for sure when a path is the same for different rules. By
using an object, we can easily compare and create a parent-child
relationship with it.
While making these changes, I deemed it necessary to also create objects
to handle Name and Id, which makes the code simpler and more robust. By
having Name and Path, we can create specific stringifiers that allow us
to customise how we render those values.
I didn’t manage to make those changes atomically, which is why this
commit makes so many changes. I found myself moving back and forth, and
making all those changes at once was the best solution I found.
I've noticed that the `StandardFormatter` was quite bloated, which made
it difficult to maintain. Understanding what each method was doing was
quite complicated. Besides, the name "Standard" doesn't mean anything,
because it doesn't say what the implementation does.
I split the `Formatter` into two different interfaces: `StringFormatter`
and `ArrayFormatter`, and I moved some code around:
* `StandardFormatter::main()` -> `FirstResultStringFormatter`
* `StandardFormatter::full()` -> `NestedListStringFormatter`
* `StandardFormatter::array()` -> `NestedArrayFormatter`
That opens up new ways of handling error messages, potentially
introducing features like `JsonStringFormatter` or `FlatArrayFormatter`
in the future.
While working on this, I removed a significant amount of unnecessary
code, which also improved my overall understanding of those formatters.
I'm not very happy with all the methods in `ValidatorDefaults`, but I
will refactor that later.
