Support multi-text symbols, or combine symbols

[dayAlone]

In my project, I need to make Symbols like on the image. Now I create 2 layers:

1. with label and icon
2. with price

And in second layer set 'text-ignore-placement': true to show price and ignore overlapping with first layer. So, after this in some cases I have result like this:

And now, I don't have any options to prevent this. If I will be able to put some array with texts to Symbol layer and style them separately it will be helpful in cases like this.

Or if I will be able to combine some layers to one for better calculation their boundaries for overlapping it will be helpful too.

[indus]

Similar: #4366

[dayAlone]

@indus Yes, similar, but not about icons :)

[1ec5]

/cc @mapbox/gl

[jfirebaugh]

Combining this with #4366 (I retitled it to generalize).