Include code and referenced text in metadata description

[mportiz08]

Bug/issue #, if applicable: 129801569, #856

Summary

Fixes a bug where the logic that populates <meta name="description"> content doesn't include the text for any referenced items.

Testing

Steps:

1. Use a link to a symbol in first paragraph abstract for a documentation page.
2. Verify that the text for the referenced symbol is now included in the <meta name="description"> tag in the resulting HTML

Checklist

Make sure you check off the following items. If they cannot be completed, provide a reason.

• [X] Added tests
• [X] Ran npm test, and it succeeded
• [X] Updated documentation if necessary

[mportiz08]

@swift-ci test

[mportiz08]

@swift-ci test