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Outliner: Hierarchy line drawing

Adds a new hierarchy line that draws to the left of collections. If the
collection is color tagged, then the hierarchy line is drawn in that
color. This is useful to see the color tag of a collection that exceeds
the vertical height of the outliner when expanded.

This also modifies the object hierarchy line drawing to match the new
collection hierarchy line, with no horizontal lines, and moved a unit to
the left. Object lines are not drawn colored.

Manifest Task: https://developer.blender.org/T77777

Differential Revision: https://developer.blender.org/D8622