Bug 993948 - [Settings] refactor to identify root panel scope inside of settings.js

- refactor to inline root panel
- move getSupportedLanguages to utils
- Not load telephony on non-phone device
- fix send_feedback asyncStorage dependency
- move keydown listener in nextTick
- refactor getSupportedLanguages with immediately-invoked function expressions (IIFE)
Merge pull request #18110 from gasolin/issue-993948

Bug 993948 - [Settings] refactor to identify root panel scope inside of ..., r=arthur