Add support for data-src attribute in IFRAME elements with src priority

[Copilot]

This PR adds support for the data-src attribute in IFRAME elements, treating it as a fallback when the traditional src attribute is empty or missing. This enables common lazy loading and progressive enhancement patterns used in modern web development.

Problem

Currently, the library only recognizes the src attribute for IFRAME elements. Many web applications use the data-src attribute for lazy loading scenarios where:

• data-src contains the actual URL to load
• src is initially empty or contains a placeholder
• JavaScript populates src from data-src when the iframe enters the viewport

Solution

Implemented attribute priority logic that:

1. Uses src when present and non-empty (highest priority)
2. Falls back to data-src when src is empty or missing
3. Maintains full backward compatibility with existing src-only iframes

Usage Examples

Traditional usage (unchanged, highest priority)

<iframe src="https://youtube.com/embed/video123" width="560" height="315"></iframe>

Progressive enhancement (src takes priority)

<iframe src="https://youtube.com/embed/hd-video" 
        data-src="https://youtube.com/embed/sd-video" 
        width="560" height="315"></iframe>

Fallback behavior (empty src uses data-src)

<iframe src="" 
        data-src="https://youtube.com/embed/video123" 
        width="560" height="315"></iframe>

Data-src only usage

<iframe data-src="https://www.youtube.com/embed/video123" width="560" height="315"></iframe>

Implementation Details

• Added kAttributeIframeDataSrc = 'data-src' constant
• Modified URL selection logic in WebViewFactory.parse():

  final dataSrc = a[kAttributeIframeDataSrc];
  final srcAttr = a[kAttributeIframeSrc];
  final src = urlFull(
    (srcAttr?.isNotEmpty == true) ? srcAttr! : (dataSrc ?? '')
  );

• Added comprehensive test coverage for all scenarios

Testing

Added test cases covering:

• Basic data-src functionality
• Priority handling when both attributes are present (src priority)
• Fallback behavior for empty/missing src
• Error handling for invalid URLs
• Backward compatibility verification

All existing functionality remains unchanged, ensuring no breaking changes for current users.

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[github-actions]

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[daohoangson]

@copilot fix failing unit test. Also, src should have a higher priority than data-src.

[Copilot]

@copilot fix failing unit test. Also, src should have a higher priority than data-src.

Fixed the priority logic to make src take priority over data-src, and updated the test cases accordingly. The commit a9315e8 addresses both the failing unit test and the priority requirement.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud