In an effort to modernize our codebase to the latest Ember version we have selected the Topic Timeline as a candidate to be refactored. The topic timeline component was originally built with `Widgets` and this PR will upgrade it to `Glimmer Components`.
The refactored timeline is hidden by default behind a group flag, `SiteSetting.enable_experimental_topic_timeline_groups`. Being part of a group included in this site setting will make the new timeline available for testing.
## Other points of interest
This PR introduces a `Draggable Modifier` available to all components, which will take the place of the existing _drag functionality_ exclusive to widgets.
It can be included like so:
```
{{draggable didStartDrag=@didStartDrag didEndDrag=@didEndDrag dragMove=@dragMove }}
```
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