A button has been introduced to launch a modal
for creating todo-lists directly from the compose box.
The modal features a form that, upon submission,
generates a message using the `/todo` syntax and the data
inputted in the form. Subsequently, the content of the compose box
is set to this message, which the user can then send.
This modal closely parallels the UI for adding a poll; therefore,
the poll and todo code has been shifted to a newly created
file named `widget_modal.ts`, and `poll_modal.ts` is now deprecated.
Co-authored-by: Sujal Shah <sujalshah28092004@gmail.com>
Fixes#29779.
