[6.0] Fix loading performance for pages with many links caused by excessive re-computation

[mportiz08]

• Explanation: Fixes performance regression where pages with large number of links may load slowly
• Scope: Impacts all pages with large numbers of links
• Issue: rdar://139214223
• Risk: Medium, code that impacts all linking to reference
• Testing: Updated unit tests, manually tested content with large numbers of links, previously tested the same cherry-picked commit on main.
• Reviewer: @hqhhuang
• Original PR: #900

[mportiz08]

@swift-ci test