After the hint by @Amire80, @Volker_E says that the CardLayout doesn't really represent the user interface concept "card" and it should be called something else. We were thinking "TabPanelLayout"?
### Process
# [x] Rename `CardLayout` → `TabPanelLayout`
## [x] Create a new `CardLayout` that just inherits `TabPanelLayout`
## [x] Rename a bunch of properties and methods in `IndexLayout`
## [x] Add deprecation warnings for everything
# [x] Update documentation on Mediawiki: [[ https://www.mediawiki.org/wiki/OOjs_UI/Index_and_Cards | Index and Cards ]] and [[ https://www.mediawiki.org/wiki/OOjs_UI/Layouts | Layouts ]].
# [x] Wait for, or fix projects that are using the old name ([[ https://github.com/search?langOverride=&q=cardlayout+org%3Awikimedia&repo=&start_value=1&type=Code | current usage ]])
## [x] {T164903}
## [x] {T164901}
## [x] {T164904}
## [x] {T164902}
## [x] {T165927}
# [ x] Remove `CardLayout`