Prefer kses to blanket esc_html on label

[getdave]

Description

This PR fixes a bug introduced when adding additional escaping to the output of blocks whereby any rich formatting or HTML would be output in it's raw form.

This PR refines the approach to use wp_kses_post which sanitizes input with allowed HTML elements for post content. This affords more flexibility whilst still warding off anything nefarious.

Kudos to @randhirexpresstech for catching and reporting this one.

Testing Instructions

1. Add Query Loop. Select default layout.
2. Below the post excerpt add x2 Post Navigation Link blocks - one for "next" and the other for "previous" (they appear as "Next" and "Previous" in the block inserter.
3. In inspector controls set both blocks to Display the title as a link and also Include the label as part of the link.
4. Add as much HTML as you can to the label. Use the rich text formatting and custom HTML.
5. Publish.
6. Check front of site. No raw HTML should be displayed unless it falls outside the bounds of what wp_kses_post deems acceptable for Post content.

Screenshots

Types of changes

Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).
• I've updated related schemas if appropriate.