Support showing constraints information besides the current size of a widget

## Problem

I use the code in https://docs.flutter.dev/ui/layout/constraints to demonstrate my issue.

In the examples below, it is not possible to know immediately the constraints that is applied on some widgets.
To find that information, we need to find in a nearest ancestor that provides the **Render object** tab or the widget that has constraints property.
It would be nice if by selecting any widget, we can answer immediately the question: "What is the constraints this widget received from its parent?"

## Expectation

I would expect something similar to **Flex explorer** tab:

Commencez par reproduire les exemples de la documentation Flutter sur les constraints dans DevTools, puis examinez l’onglet Flex explorer existant comme le précédent indiqué le plus proche. Le travail est terminé lorsque la sélection de n’importe quel widget affiche les constraints qu’il a reçues de son parent en plus de sa taille actuelle.

Rédigé par le modèle d'indexation à partir du texte de l'issue.