Implement viewport meta parsing in HTMLMetaElement and apply to window dimensions

[yorkie]

Implement parsing of the meta[name="viewport"] tag in HTMLMetaElement according to the MDN specification.

Requirements:

• Parse the content attribute of <meta name="viewport">, extracting values such as width, height, initial-scale, maximum-scale, minimum-scale, and user-scalable following the rules and supported keywords as described by the MDN documentation.
• Ensure the parser is robust, handling whitespace, missing values, and invalid input gracefully.
• After parsing, apply the parsed width and height values to control the window's logical dimensions.
• Support dynamic updates if the meta tag changes after initial parsing.
• Provide tests for various viewport meta tag scenarios and expected window size changes.
• Document the implementation and any limitations or differences from browser behavior.

Acceptance Criteria:

• HTML containing <meta name="viewport" content="width=640,height=480"> sets window width to 640 and height to 480.
• Changing the meta tag at runtime updates window dimensions accordingly.
• Parsing is consistent with behavior described in MDN and common browser implementations.
• Tests pass for a variety of valid and invalid viewport meta configurations.