## Summary of the Pull Request
This PR adds a global "language" setting, which may be set to any supported BCP 47 tag.
Additionally a ComboBox is added to the settings UI under "Appearance", listing all languages with their localized names.
This PR introduces one new issue: If you change the language while the app is running, the UI will be in a torn state, as not all UI elements refresh automatically if the `PrimaryLanguageOverride` is changed.
## PR Checklist
* [x] Closes#5497
* [x] I work here
* [x] Tests added/passed
* [ ] Documentation updated. If checked, please file a pull request on [our docs repo](https://github.com/MicrosoftDocs/terminal) and link it here: #xxx
* [x] Schema updated
## Validation Steps Performed
* UI language changes when changing the "language" in settings.json before starting WT / while WT is running. ✔️
* "language" field is removed from settings.json if "Use system default" is selected. ✔️
* "language" field is added or updated in settings.json if any other language is selected. ✔️
* Removes qps- languages if debugFeatures is false. ✔️
* Correctly refreshes all UI elements with the new language. ❌
This pull request adds an appearance configuration object to our
settings model and app lib, allowing the control to be rendered
differently depending on its state, and then uses it to add support for
an "unfocused" appearance that the terminal will use when it's not in
focus.
To accomplish this, we isolated the appearance-related settings from
Profile (into AppearanceConfig) and TerminalSettings (into the
IControlAppearance and ICoreAppearance interfaces). A bunch of work was
done to make inheritance work.
The unfocused appearance inherits from the focused one _for that
profile_. This is important: If you define a
defaults.unfocusedAppearance, it will apply all of defaults' settings to
any leaf profile when a terminal in that profile is out of focus.
Specified in #8345Closes#3062Closes#2316
