Show underline warning in settings JSON file when value matches default

<!-- ⚠️⚠️ Do Not Delete This! feature_request_template ⚠️⚠️ --> <!-- Please read our Rules of Conduct: https://opensource.microsoft.com/codeofconduct/ --> <!-- Please search existing issues to avoid creating duplicates. --> <!-- Describe the feature you'd like. --> When working with any of the `settings.json` files (user or workspace) It would be amazing to know if you are overriding a property with the exact same value as the default settings. Maybe highlighting it. Then we can avoid duplicating configurations and we can keep our settings with just the necessary overrides. ## Motivation Keep settings to the bare minimum aligns perfectly with the vscode minimal philosophy, so having a file where we just tweak what it's necessary feels as a crucial feature. ## Implementation A simple underline warning to the setting that has the same value as the default would be enough to tell the user that what they are writing is redundant.