Image: Ensure consistent image block rendering between editor and frontend

[himanshupathak95]

Fixes: #67088

What?

Changes the CSS property of image blocks from max-width: 100% to width: 100% to ensure consistent rendering between editor and frontend.

Why?

• Low-resolution images were displaying inconsistently between editor and frontend
• This broke the WYSIWYG (What You See Is What You Get) experience
• Users were getting confused by different image sizes in editor vs published view
• Prior implementation with max-width allowed images to shrink below their container width

How?

• Modified the CSS for .wp-block-image img selector
• Changed max-width: 100% to width: 100%
• Maintained height: auto for proper aspect ratio
• Preserved existing animation and visibility state styles

Testing Instructions

1. In the site editor, Add an image block
2. Upload or select a low-resolution image (e.g., 300x200px)
3. Observe the image size in editor
4. Save and preview/publish the post
5. Compare the image dimensions between editor and frontend

Screencast

Before fix:

img-block-width-fix-before.mov

After fix:

img-block-width-fix-after.mov

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