Use <strong> tag instead of <b> tag in `Walker_Comment::html5_comment`

[itowhid06]

It is well documented that when some text is bolded using the <b> tag, it will come to no benefit for users using screen readers. This patch aims to fix that in an instance of html5_comment method in Walker_Comment.

[SergeyBiryukov]

Thanks for the patch! The <b> tag was introduced in [24539] / #24522 and is only used here as a wrapper for comment author name, not to signify importance.

Per the ​HTML standard, this appears to be valid usage:

The b element represents a span of text to which attention is being drawn for utilitarian purposes without conveying any extra importance and with no implication of an alternate voice or mood, such as key words in a document abstract, product names in a review, actionable words in interactive text-driven software, or an article lede.

Per ​MDN web docs, too:

The HTML Bring Attention To element (<b>) is used to draw the reader's attention to the element's contents, which are not otherwise granted special importance.
...

• Use the <b> for cases like keywords in a summary, product names in a review, or other spans of text whose typical presentation would be boldfaced (but not including any special importance).
• Do not confuse the <b> element with the <strong>, <em>, or <mark> elements. The <strong> element represents text of certain importance, <em> puts some emphasis on the text and the <mark> element represents text of certain relevance. The <b> element doesn't convey such special semantic information; use it only when no others fit.

[afercia]

This ticket was discussed during today's accessibility bug-scrub.

While it's true the usage of a <b> element in this case is not incorrect, it is also true that right now the commenter username has no specific semantics. For example, screen readers would read it as normal text. It would be nice to add some semantic, not sure a <strong> element would be appropriate though. Also, there are backwards compatibility concerns. Moving to future release for now, pending some research and investigation.