Make Value Objects and DTOs easier to work with and to debug

[bwaidelich]

Our Value Objects and DTOs are strict by design.
But this makes it harder to use them in non-PHP land (like Fusion or Fluid). Besides debugging stack traces gets really hard.

Suggestion

• Implement the __debugInfo() magic method where it makes sense to improve debugging output
• Implement the __toString() magic methods where it makes sense (specifically in value objects that represent a single simple type)
• Create a linter rule to prevent explicit string casts in our code base ((string)$someValueObject)
• Create a linter rule to prevent implicit string casts in our code base (e.g. foo($someValueObject) where function foo (string $bar) {})

Notes

• @skurfuerst suggested to return the value of the VO for objects that represent a single value and some debugging string for objects that contain multiple properties (e.g. Node[aggregateId: ..., workspace: ....]) such that they are not converted by accident – for the latter we can implement __debugInfo() to provide more details
• To prevent the implicit casting it should be enough to enforce the declare(strict_types=1); declaration in all PHP files of the core

[mhsdesign]

Also i think we should leverage the string casts in fusion again for node.name instead of using node.name.value as elaborated here: #4156 (comment)

The thing is the to get the site entity name we use site.name as its not a dto there. This is super confusing even for us and causes lots of bugs in the past (#5236 ...)