Title attributes on abbreviations are only available to a minority of users. The
best option is to avoid unnecessary abbreviations when possible. In the other cases,
use an `<abbr>` element (which provides a hint to user agents on how to announce
and display the abbreviation) and provide an expansion in plain text on first use.
- `readme.html`: improves abbreviations and removes unnecessary `title` attributes
- options-general: removes unnecessary abbreviations and improves the remaining ones
- customizer schedule changeset date: removes unnecessary abbreviations and improves the remaining ones
- posts table date: uses a `span` element instead of an `abbr` element because this is not an abbreviation
Fixes#46980.
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