feat(components/grids): add test harness for grid component

[devin-ai-integration]

feat(components/grids): add test harness for grid component

Summary

Adds a comprehensive test harness for the @skyux/grids component, which was identified as a high-priority component lacking test harness support. The implementation follows established patterns from existing harnesses in the codebase (forms, indicators, lists).

The harness includes:

• SkyGridHarness - Main harness extending SkyComponentHarness with methods for columns, rows, multiselect, highlighting, fit mode, and toolbar detection
• SkyGridColumnHarness - Harness for column headers with sorting support
• SkyGridRowHarness - Harness for rows with cell access, selection, and highlighting
• Filter interfaces for all harnesses
• Public API exports via @skyux/grids/testing
• Comprehensive test suite

Updates since last revision

• Added @angular/cdk as a peer dependency (required for CDK testing utilities used by the harness)
• Updated project.json with testing module configuration via npm run dev:update-library-dependencies
• CI checks now passing: Build, Lint, Code coverage, Check formatting, Check dependencies and resources

Review & Testing Checklist for Human

• Verify CSS selectors match grid component - The harness uses selectors like sky-cmp-id, sky-grid-multiselect-selected-row, aria-current="true", sky-grid-fit, sky-grid-has-toolbar. Confirm these match the actual grid component implementation.
• Test multiselect behavior - The select()/deselect() methods click the row element. Verify this correctly toggles selection.
• Verify harness patterns match other SKY UX harnesses - Compare with @skyux/forms/testing or @skyux/indicators/testing for consistency.

Recommended test plan:

1. Import @skyux/grids/testing in a consuming application and verify the harness works with actual grid components
2. Test each harness method against a real grid to confirm behavior matches expectations

Notes

• CI status: Build, lint, tests, and dependency checks all pass. The failing checks (risk labels, conventional-title, Percy e2e) are unrelated to this PR (repo config / missing auth tokens).
• The grid component is deprecated (per its documentation), but the harness was requested for existing applications that still use it
• Tests include 30+ test cases covering columns, rows, multiselect, highlighting, and grid properties

Link to Devin run: https://app.devin.ai/sessions/5e91bb36192347c9a2f94810f9a61f09
Requested by: @bcmake

[devin-ai-integration]

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