Display metrics graph as series of disconnected line segments

[monicawoj]

For delta profiles, the metrics graph should be visualized differently. Currently, it shows a single line of connected points. Because each point actually represents a range of time, it would be more accurate to visualize this as a series of disconnected horizontal line segments. Each line segment spans the duration of the step.

[monicawoj]

@brancz if you have more details here that would be helpful, please feel free to add!