This fixes a crash caused by Narrator starting *before* terminal.
Fixes#2907.
For context,
```
// We must initialize the main thread as a single-threaded apartment before
// constructing any Xaml objects. Failing to do so will cause some issues
// in accessibility somewhere down the line when a UIAutomation object will
// be queried on the wrong thread at the wrong time.
// We used to initialize as STA only _after_ initializing the application
// host, which loaded the settings. The settings needed to be loaded in MTA
// because we were using the Windows.Storage APIs. Since we're no longer
// doing that, we can safely init as STA before any WinRT dispatches.
```
cc371b0531