Trac: Merge "Text Changes" component with the "ui-copy" focus

[SergeyBiryukov]

Background: #4610.

The ui-copy focus was added to Trac in [9076]. Apparently the name is not clear enough for non-native English speakers and causes some confusion: ​#WP51080 is just a recent example, but there were some earlier examples too.

There is also a "Text Changes" component that is no longer actively used and can be retired in favor of the focus, per comment:2:ticket:4850, as text changes can belong to a particular component or span across multiple components.

Based on the above, I think the following would make sense:

• Rename the ui-copy focus to text-changes to clarify its purpose.
• Remove the "Text Changes" component in favor of the focus.