fix: Properly include shapes when toggling legend visibility

[camdecoster]

Description

Include shapes with legendgroup specified when handling legend visibility toggling.

Closes #6771.

Changes

• Update shape default coercion to properly set legend, legendgroup attributes
• Update filtering for shapes when toggling legend visibility
• Add test

Screenshots/Videos

Before:

Screencast.From.2026-05-28.17-12-40.mp4

After:

Screencast.From.2026-05-28.17-12-04.mp4

Notes

• There were two bugs:
  • Shapes with a legendgroup and also showlegend as false were getting filtered out of the check for handling legend clicks to toggle visibility
  • Certain shape attributes were gated behind a check on showlegend, so those attributes weren't getting populated
• This update matches the behavior of traces and legendgroup visibility toggling

[emilykl]

LGTM 🚀

[emilykl]

hold up @camdecoster -- any chance the failing image test is related to these changes, since the failure is that some images are not showing up? Maybe shapes and images share some coercion logic.

edit: Never mind, unrelated

[zdimension]

Thanks!