Deprecate core_course\output\activity_information class and move its code to two
new classes: core_course\output\activity_completion and core_course\output\activity_dates.
In this process refactor activity_completion improving readability and and also deprecate
renderer_base::activity_information() and core_course_renderer::render_activity_information().
Add a new method for activity_header that determines the heading level
depending on whether the theme displays a heading for the activity
header (usually a h2 heading with the activity name).
E.g. in Boost, the activity name is already being displayed in a
heading. So page headings can be rendered as h2. However, on Classic,
the activity name is being displayed as a h2 heading. So headings need
to be adjusted for the activity pages.
The current manual completion button triggers an event to alert the page
of any completion change. This event is capture in the course page by
the core_courseformat/local/content module but it was ignored when this
happens in an activity page. Now the activity header has its own
component to capture this event and support possible future reactive
actions.