Post Author: Switch byline to use kses so that rich text elements are rendered correctly

[andrewserong]

What?

Fixes: #40600

Why?

Currently, the Byline field of the Post Author block renders HTML elements added via the rich text controls in the editor as the raw escaped HTML elements on the front end of a site (e.g. <strong>my byline</strong>).

For server-rendered blocks that render out rich text stored in an attribute, we need to use wp_kses_post instead of esc_html so that the rich text elements (e.g. <strong>, <em>, etc) are rendered correctly, while still ensuring that illegal elements (e.g. script) are stripped. This approach follows eariler PRs like: #38649

How?

In the Post Author block, swap esc_html for wp_kses_post.

Testing Instructions

1. In the site editor, go to update the single template, and add a Post Author block and include a byline for the post author.
2. Use the rich text controls to add bold or emphasised text.
3. Prior to this PR, on the front end of the site, the raw characters of the HTML tags are output
4. After this PR, the rich text elements should be rendered correctly

Screenshots or screencast

Before	After

[dsas]

Hey Andrew! This tests well for me and the PR makes sense 👍

[glendaviesnz]

Works as advertised for me. I also checked with contributor role and all the formatting works as expected still in preview for them.

[andrewserong]

Thanks for the reviews!

[gziolo]

I cherry-pick this PR for WordPress 6.0 RC2 release with 2949638.