Improve consistency in metadata display strings

[gregoriopellegrino]

While gathering feedback on the Accessibility Metadata Display Guide 2.0, we noticed some inconsistencies in how features are described. For example, in the Navigation section (https://w3c.github.io/publ-a11y/a11y-meta-display-guide/2.0/draft/guidelines/#nav-examples), some strings begin with "Contains..." while others directly describe the feature (e.g. "Index provides links...").

We think it would be valuable to establish a consistent pattern for all descriptive strings across the guide. This would make the information more predictable and easier to scan, while also helping with localization efforts.