Implementation for Issue plotly#5099 adds three new legend components that show
unique values from marker attributes (color, size, symbol) rather
than trace-based legends.

New components:
- colorlegend: displays unique color values as swatches
- sizelegend: displays size ranges as graduated circles
- symbollegend: displays unique marker symbols

Features:
- Click to toggle visibility of points with that attribute value
- Support for multiple legends (colorlegend, colorlegend2, etc.)
- Configurable positioning, styling, and orientation
- Works with scatter and scatter-variant traces