Support automatic reset of expanded arrays/objects when DefaultExpand setting changes

[dmackdev]

This PR enables automatic reset of expanded arrays/objects when the DefaultExpand setting changes between two frames. This is enabled by default, but can be controlled via configuration method JsonTree::auto_reset_expanded(bool).

Automatic reset of expanded arrays/objects eliminates some boilerplate and the current burden on the programmer to currently do this manually via JsonTreeResponse::reset_expanded(egui::Ui). This must be done in order to have the JsonTree automatically expand/collapse those arrays/objects to respect the DefaultExpand setting, e.g. to only expand and highlight search term matches within the tree.

This works by storing (temporarily, not persisted) the hash of the DefaultExpand value in egui's IdTypeMap (superficial widget state) against the JsonTree's Id. When this value changes between two frames, we know to reset the expanded arrays/objects to respect the changed DefaultExpand setting in the next frame. Additionally, a unit struct is also stored temporarily, whose presence indicates that a reset is required. Resetting expanded state is now done lazily, as each node in the tree renders, instead of all at once via the response.

Future work could extend this concept to allow the programmer to register "reset expanded keys" on the JsonTree, which could trigger a reset of the arrays/objects when the key changes between two frames (similar to the dependencies array in React's useEffect). This way, the result of a button.clicked() call could be registered to trigger a reset of the expanded arrays/objects.