feat: Action Bar

[tanugarg04]

Description
Adds ChartActionBar as a new child component for Line charts in the S2 package. When a user clicks a data point, a floating contextual toolbar appears near that point with user-defined action buttons. The bar supports overflow truncation (actions beyond available space collapse into a ··· panel), drag-to-reposition, and an emphasized visual style via isEmphasized.

New public API:

— render-null stub accepted as a child of
children: (datum, close) => ReactElement[] — render function receiving the clicked datum and a close callback
isEmphasized?: boolean — accent background with white icon treatment, matching the RS ActionBar emphasized style
maxActions?: number — hard cap on inline actions before overflow (default 4; space is the primary driver)
onClearSelection?: () => void — called when the bar is dismissed
Behavior:

Interactive behavior (selection ring, hover signals, clear-on-close) mirrors ChartPopover
If both ChartActionBar and ChartPopover are children of the same Line, a runtime warning is emitted and the ChartActionBar takes precedence for left-click. A right-click ChartPopover can coexist
Bar is draggable so users can reposition it if it overlaps content
Related Issue
N/A — new feature scoped to the S2 package (@spectrum-charts/react-spectrum-charts-s2)

Motivation and Context
Charts often need contextual actions tied to a selected data point (annotate, comment, export). The existing ChartPopover handles arbitrary content but requires the user to build their own action layout. ChartActionBar provides a purpose-built, accessible toolbar pattern that matches the Spectrum 2 design — floating near the point, space-aware, and dismissible.

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.