Docs: Add missing @return descriptions in bundled themes

[huzaifaalmesbah]

Several functions in bundled themes (Twenty Fourteen, Twenty Seventeen, Twenty Nineteen, Twenty Twenty, and Twenty Twenty-One) are missing descriptions for their @return tags, or are missing the tags entirely.

Files updated:

• wp-content/themes/twentytwenty/functions.php
• wp-content/themes/twentytwenty/inc/template-tags.php
• wp-content/themes/twentytwenty/classes/class-twentytwenty-customize.php
• wp-content/themes/twentyseventeen/inc/template-functions.php
• wp-content/themes/twentyseventeen/inc/template-tags.php
• wp-content/themes/twentytwentyone/inc/template-functions.php
• wp-content/themes/twentyfourteen/functions.php
• wp-content/themes/twentyfourteen/inc/widgets.php
• wp-content/themes/twentynineteen/functions.php
• wp-content/themes/twentynineteen/classes/class-twentynineteen-svg-icons.php
• wp-content/themes/twentynineteen/inc/customizer.php
• wp-content/themes/twentynineteen/inc/template-functions.php

This PR addresses missing or incomplete @return tag documentation in several bundled themes.

Changes include:

• Adding descriptions to @return tags in functions.php and other include files for Twenty Twenty, Twenty Seventeen, and Twenty Twenty-One.
• Adding missing @return tags and descriptions in Twenty Fourteen and Twenty Nineteen.

Trac ticket: https://core.trac.wordpress.org/ticket/64277

[palak678]

I went through the updated docblocks in the bundled themes and adding @return descriptions look good. This definitely improves clarity and brings the comments more in line with the coding standards.

[westonruter]

In 61302:

Bundled Themes: Add missing @return tags and descriptions.

Developed in ​https://github.com/WordPress/wordpress-develop/pull/10533

Props huzaifaalmesbah, sabernhardt, palak678, westonruter.
See #64224.
Fixes #64277.

[westonruter]

In 61319:

Twenty Twenty: Fix typo and improve param description for twentytwenty_read_more_tag().

Follow-up to [61302].

Props sabernhardt.
See #64277, #64224.