feat(fast-html): support boolean attributes that have conditions

[mohamedmansour]

Summary

Adds support for boolean attributes with comparison expressions in @microsoft/fast-html. Previously, attribute bindings only supported simple property access (e.g., {{type}}). Now, expressions like ?data-active="{{activeGroup == currentGroup}}" are correctly resolved — the boolean attribute is toggled based on the result of the comparison.

Changes

• template.ts — When processing attribute bindings, the code now checks if the value is a comparison expression (via getExpressionChain). If the operator is not a simple "access", it routes through expressionResolver instead of bindingResolver, enabling condition evaluation for attributes.
• attribute.spec.ts — Added a new Playwright test ("boolean attribute with comparison condition") that validates the attribute is present when the condition is true, removed when the condition becomes false, and re-added when it becomes true again.
• index.html — Added a test-bool-condition fixture using ?data-active="{{activeGroup == currentGroup}}" with pre-rendered SSR shadow DOM.
• main.ts — Registered TestBoolCondition component with activeGroup and currentGroup observed attributes.

What still works with attributes

• Simple property access bindings like type="{{type}}" continue to use the existing bindingResolver path — no behavior change.
• The disabled static attribute still renders correctly.
• SSR pre-rendered shadow roots with data-fe-b-* markers hydrate as before.

[janechu]

This script should not be in the head, can we place this back to the end of the body?.

[janechu]

Just as a precaution, I think these strings should be different between the activeGroup and currentGroup so that we don't get false positives.

[janechu]

Feels like we should update the expressionResolver to resolve regular access paths if it does not already and simplify this to just call the expressionResolver without an if/else check.