Move TerminalSettings object from TerminalSettings project
(Microsoft.Terminal.Settings) to TerminalApp project. `TerminalSettings`
specifically operates as a bridge that exposes any necessary information
to a TerminalControl.
Closes#7139
Related Epic: #885
Related Spec: #6904
## PR Checklist
* [X] Closes#7139
* [X] CLA signed
* [X] Tests ~added~/passed (no additional tests necessary)
* [X] ~Documentation updated~
* [X] ~Schema updated~
## Validation Steps Performed
Deployed Windows Terminal and opened a few new tabs.