[Suggestion] Toggle Options 'charHasUprightVerticalOrientation'

Nobody has claimed this yet.

## Motivation
Korean language is much better visibility in "symbol placement: 'line'" case below.
I think Korean does not need to rotate char some case.
Is it possible to make toggle option?

Screenshot from South Korea's major map. (Kakao map)

[http://kko.to/wo6oWUy0p](http://kko.to/wo6oWUy0p)

## Design Alternatives

Toggle options from instance init. "charHasUprightVerticalOrientation"
```
new mapboxgl.Map({
// boolean
charHasUprightVerticalOrientation: false
});
```

## Code Points
https://github.com/mapbox/mapbox-gl-js/blob/master/src/symbol/shaping.js#L607
https://github.com/mapbox/mapbox-gl-js/blob/master/src/util/script_detection.js#L119

Start with src/symbol/shaping.js around line 607 and src/util/script_detection.js around line 119 to trace how upright vertical orientation is determined. Then inspect the Map instance initialization options and existing symbol-placement tests; done means the proposed charHasUprightVerticalOrientation toggle controls Korean character rotation for line placement without changing the default behavior.

Written by the indexing model from the issue text.