feat(api): expand Features API with quality tool flags

[teogor]

Description

This PR expands the core Features API in winds-api to support new opt-in flags for project quality tools. This is a foundational change that enables integrated configuration for Spotless, Dokka, and API Validation.

Changes

[winds-api]

• Features.kt: Added apiValidator, dokka, and spotless Boolean properties with comprehensive KDoc documentation.
• Winds.kt: Updated isEnabled(WindsFeature) logic to resolve the new flags from the features block.

[winds-gradle-plugin]

• FeaturesImpl.kt: Updated the data class implementation to include the new properties with default values (false).

Impact

• No breaking changes. Deprecated windsFeatures and publishingOptions are retained for backward compatibility as requested.
• Enables granular control over quality tool application through the winds {} extension.

Verification

• Verified by running ./gradlew build and checking for binary compatibility with ./gradlew apiCheck.