Only use one term to mean one thing across the UI and documentation

Collect terms and concepts used in the UI and pick one term to use for one concept. Then, use that term consistently in the UI and documentation.

Explain the chosen terms in https://doc.qt.io/qtdesignstudio/studio-terms.html and document the reasons for picking a term (and list terms to avoid) in a new topic similar to this one: https://doc.qt.io/qtcreator-extending/qtcreator-ui-text.html#common-qt-creator-terms