This started out as "replace the Collapsible in the timeline so that the tooltips for the timestamps work again" and turned into "I don't understand half of what this component is doing, let's give it some love."
Cleaned up props
Timeline.stages now only accepts valid stages (i.e. stages with a date). Consumers should be responsible for filtering.
Timeline.withoutPreviousDate became Timeline.showDurations, because a) "previous date" was a weird description for a time distance between two items in the timeline sequence and b) I think positively-framed props ("show this thing") are easier to reason about than negatively-framed props ("don't show this thing")
TimelineStage.expanded became TimelineStage.expandedByDefault, to avoid any confusion over who is in control of the collapsible state
Restructured component
TimelineMeta was a weird abstraction for part of the item label we show for each stage, so now it has become TimelineStage
There was a lot of unnecessary <div /> nesting, this has been flattened
Refactored Collapsible to use Collapse
Cleaned up styles
Improved Storybook coverage
Screenshots
Tooltip functionality restored!
Batch spec execution timeline
Code intel upload timeline
Code intel audit log timeline
Test plan
Validated tooltips are visible again, manually tested timeline in the Batch Changes modal. There isn't Storybook coverage for the other instances of Timeline used across Code Intel, and I don't have Code Intel set up locally, but I was able to inspect some from the app preview and they still looked good!
