Command autocomplete doesn't consider parts after a slash

The bug

In 20w15a command autocomplete was changed to also consider parts after an underscore. Text after a period or slash however, is not included in the suggestion results. This causes some confusing results with the attribute IDs

How to reproduce

1. Type "/attribute @s hea"
   generic.max_health is correctly suggested
2. Type "/attribute @s max"
   generic.max_health is not shown