Steps to reproduce:

- Create 2 projects: `Project1` and `Project2`
- Enable sub-tasks
- In Project1 create a task, name it `1`.
- In task 1 add a subtask, name it `1:1`.
- In task 1:1 add another subtask, name it `1:1:1`.
- Go to Timesheet app > add lines for each task.
- The lines display name are `Project1 / 1`, ...
- Go back to task 1, edit the task project to Project2 and save.
- The subtasks will have their project_id also set to Project2.
- Go to Timesheet app.

Issue:
Tasks `1` and `1:1` will have their display names updated to `Project2 / 1` and `Project2 / 1:1`. However, task `1:1:1` is displayed as `Project1 / 1:1:1`, meaning that the `project_id` field was never updated.

This happens because of the way changed fields propagate to immediate children, but not to grandchildren, which is intended behaviour.

Solution:

`_compute_project_id` is also called onchange, meaning that we can use it to update account lines with an outdated project value with the new value.

opw-3018301

Forward-Port-Of: odoo/odoo#109263
Forward-Port-Of: odoo/odoo#106164