Maybe rename `TextUiWriter` to `UiTextWriter`

In bevyengine/bevy-website#1782, it was mentioned that the (WIP) migration guide for the text rework (#15591), refers to
`UiTextWriter` instead of the actual name we have right now `TextUiWriter`.

I think it is obvious how this mistake slipped in there, `UiTextWriter` is a more intuitive name. It is (in my opinion) better to have a type alias' name have something appended or prepended to the name, instead of plopping something in the middle (like we have right now, where we added `Ui` in between instead of at the front).

The same thing goes for `TextUiReader`, I think they should both be renamed.

Let me know what you think, just wanted to ask this before I start writing some stuff for the website.

Start by locating the definitions and usages of TextUiWriter and TextUiReader, then compare them with the UiTextWriter references in the migration guide for text rework (#15591) and bevy-website#1782. Confirm the intended names and identify all affected references; done means both aliases and their references consistently use the agreed naming.

Written by the indexing model from the issue text.