Docs: Add @param and @return description for maybe_hash_hex_color().

Follow-up to [20936], [21354], [37283].

Props rollybueno, SergeyBiryukov.
See #63166.

git-svn-id: https://develop.svn.wordpress.org/trunk@60709 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-includes/formatting.php

@@ -6432,8 +6432,9 @@ function sanitize_hex_color_no_hash( $color ) {
  *
  * @since 3.4.0
  *
- * @param string $color
- * @return string
+ * @param string $color The color value to add the hash prefix to. Can be with or without a #.
+ * @return string The color with the hash prefix if it's a valid hex color,
+ *                otherwise the original value.
  */
 function maybe_hash_hex_color( $color ) {
 	$unhashed = sanitize_hex_color_no_hash( $color );