Fixes https://github.com/flutter/devtools/issues/8553
Context:
A Flutter web customer with a large widget tree was getting a stack
overflow error when they toggled on "show implementation widgets" in the
Flutter DevTools Inspector. This is because building the JSON tree
recursively was hitting Chrome's stack limit.
This PR creates the JSON tree **iteratively** if the `getRootWidgetTree`
service extension is called with `fullDetails = false` (which is what
DevTools uses to fetch the widget tree).
For all other instances of creating a widget JSON map (for example, when
fetching widget properties) the recursive implementation is used. This
allows properties provided by subclasses implementing `toJsonMap` to be
included in the response.
Note: Because with this change `toJsonMap` is only called when
`fullDetails = true` and `toJsonMapIterative` is only called when
`fullDetails = false`, this PR partially reverts the changes in
https://github.com/flutter/flutter/pull/157309.
21bea32f66