Fill in Selected Lollipop LineMark in SingleLineLollipop

[CheerfulSatchel]

Greetings, reviewer!

This PR fills in and slightly expands the currently selected lollipop LineMark. This adds a visual aid for users to more clearly and distinctly see which LineMark they are currently viewing.

Changes

• Data.swift: Made the Sale struct conform to the Equitable protocol. Any data passed to this type of chart should conform to the Equitable protocol in order to easily compare the current selected lollipop LineMark and each LineMark rendered on the Chart.
• SingleLineLollipop.swift: Added the lollipop color picker. If the lollipop is currently over the LineMark, it will fill in and slightly expand said LineMark. I wanted to call LineMark's .symbol property with a ternary operator - However, there is no mechanism for supplying a .symbol with a ChartSymbolShape that fills in the shape. This meant that I could not write a ternary operator that chose between the filled in circle (some View) and unfilled in circle (some ChartSymbolShape) as the types did not match. Hence why I pulled baselineMarker out into its own function first before conditionally deciding which .symbol function to call with a parameter type of either some View or some ChartSymbolShape.

Before

After

Thank you!

[CheerfulSatchel]

Psst, is this repo still being maintained? My dusty PR is indeed dusty 😎