Notifications now include the source entity. This is useful for
callbacks that are responsible for more than one widget.
Part of #19236
This is an incremental change only: I have not altered the fundamental
nature of callbacks, as this is still in discussion. The only change
here is to include the source entity id with the notification.
The existing examples don't leverage this new field, but that will
change when I work on the color sliders PR.
I have been careful not to use the word "events" in describing the
notification message structs because they are not capital-E `Events` at
this time. That may change depending on the outcome of discussions.
@alice-i-cecile
# Objective
Because we want to be able to support more notification options in the
future (in addition to just using registered one-shot systems), the
`Option<SystemId>` notifications have been changed to a new enum,
`Callback`.
@alice-i-cecile
# Objective
This PR introduces Bevy Feathers, an opinionated widget toolkit and
theming system intended for use by the Bevy Editor, World Inspector, and
other tools.
The `bevy_feathers` crate is incomplete and hidden behind an
experimental feature flag. The API is going to change significantly
before release.
---------
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
