Yaml support

[horner]

See issue:
#7009

Overview

This PR implements YAML support for SurveyJS Creator, allowing users to work with survey definitions in YAML format as an interchangeable alternative to JSON.

Why YAML?

• Human-friendly: YAML is significantly easier to read and write by hand than JSON, especially for complex survey structures.
• Better for version control: Line-based diffs in Git are easier to interpret and resolve in YAML.
• DevOps and infrastructure alignment: YAML is the de facto format for configuration in modern ecosystems (e.g., Kubernetes, GitHub Actions, Ansible).

Features Added

🔧 Core YAML Utilities

• SurveyYAML utility class with parsing, stringification, and validation methods
• Format conversion between JSON and YAML with error handling
• Custom formatting options for YAML output (indentation, line width, etc.)

📝 Creator API Extensions

New properties and methods added to SurveyCreatorBase:

// Get/set survey as YAML
creator.yamlText = yamlString;
const yaml = creator.yamlText;

// File operations
creator.exportToYAMLFile('survey.yml');
creator.importFromYAMLFileDOM();

// Utility methods
const yaml = creator.toYAML();
creator.fromYAML(yamlString);

🎛️ YAML Editor Plugin

• New editor tab extending the existing JSON editor functionality
• Real-time YAML validation with error reporting
• Toolbar actions for import/export/copy operations
• Seamless integration with the existing tab system

📁 File Import/Export

• Native file operations for .yaml and .yml formats
• Browser-compatible download/upload functionality
• Action creators for UI integration
• Error handling for invalid files

Example Usage

Basic YAML Survey Definition

title: Customer Satisfaction Survey
description: Please help us improve our service
pages:
  - name: page1
    elements:
      - type: text
        name: firstName
        title: First Name
        isRequired: true
      - type: rating
        name: satisfaction
        title: Overall Satisfaction
        rateMin: 1
        rateMax: 10

Programmatic Usage

// Convert existing JSON survey to YAML
const yamlString = SurveyYAML.jsonToYaml(jsonString);

// Parse YAML survey definition
const surveyObj = SurveyYAML.parse(yamlString);

// Round-trip conversion
creator.yamlText = yamlString;
const backToYaml = creator.yamlText;

Implementation Details

• Leverages js-yaml library for robust YAML parsing
• Maintains backward compatibility - all existing JSON APIs unchanged
• Follows existing patterns in the codebase for consistency
• Comprehensive error handling with user-friendly messages
• Full Unicode support for international content

Testing

• ✅ 10/10 manual tests passing covering all functionality
• ✅ Round-trip conversion validation (JSON ↔ YAML ↔ JSON)
• ✅ Error handling for invalid YAML syntax
• ✅ Special characters and Unicode support
• ✅ File operations simulation
• ✅ Integration tests for creator API

Documentation

• 📚 Complete API documentation with examples
• 🔍 Usage examples for HTML, React, and Node.js
• 📋 Sample YAML surveys demonstrating features
• 🛠️ Migration guide from existing JSON surveys

Browser Compatibility

Works in all modern browsers supporting:

• ES6+ features
• File API for import/export
• Blob API for downloads