Implement document.createComment() in client/dom and related files

[yorkie]

Implement the DOM API document.createComment() in the JSAR runtime, specifically within the client/dom directory and any related files.

Requirements:

• Add the createComment() method to the Document implementation, matching the standard Web API signature.
• Ensure it returns a Comment node with correct node type and value.
• Update or create the necessary Comment node class if it does not exist.
• Integrate the new Comment node into the DOM tree and serialization logic as appropriate.
• Add tests to verify comment node creation, tree insertion, and serialization.
• Update documentation if needed.

Affected areas:

• client/dom/document.*
• client/dom/comment.* (if applicable)
• Any other DOM-related files necessary for full support

References:

• MDN: document.createComment
• DOM Standard

Acceptance Criteria:

• document.createComment('text') returns a Comment node with value 'text'
• The Comment node can be inserted into the DOM tree
• Serialization (outerHTML, innerHTML, etc.) correctly handles comment nodes
• Tests pass for comment node creation and usage