Uptil now, users could add tasks to a todo widget only after creating
it through the `/todo` command in the compose box.
Users can now add an initial list of tasks using the `/todo` command,
with each task on a new line in the compose box, where the 1st `:`
would separate a task from its (optional) description. Example:
`/todo\nTask1:description1\nTask2 without description`.
Fixes part of #20213.
Users can now name task lists by providing the task list title in the
`/todo` command on the same line. Example: `/todo School Work`. If no
title is provided by the user, "Task list" (which is also the
placeholder) is used as default.
The author of a task list can later edit / update the task list title
in the todo widget, just like the question in the poll widget.
Fixes part of #20213.
The schema now ensures extra data is validated according to the widget
type. This also makes it easier to modify the extra data for any widget
or add new widget types in the future.
