Support Polygon for tile_bounds !

Nobody has claimed this yet.

## Motivation

When working with raster layers we often have parse data or not `square` source, resulting in really poor performance (because mapbox-gl-js is trying to load tiles that don't exist.)

I understand that support polygons (or even Multipolygons) will also impact the performance but I'd like to see if this could be an alternative.

## Design Alternatives

> "do nothing" an option

Sure this is not something that have to be implemented but will be a nice to have 🙉

## Design

Not sure if @mourner have a really light and performance `polygon` intersection algorithm we could use 😄

The best option will be to keep this as invisible as possible for the user, which will either pass a `[number, number, number, number]` or a geojson like polygon feature representing the bounds.

### Concepts

> Where do the concepts set new precedents?

Well this could set some precedents where user could ask for more feature type support (e.g multi-poylgon) or to support this kind a `bounds` in other api.

Thanks

👼 🙏

I'll be happy to start a sketch PR... but might not be the best person to do it

Start by tracing how tile_bounds is handled for raster layers and how mapbox-gl-js decides which tiles to load. The issue names no files, tests, or implementation entry points, and its proposed polygon input and intersection behavior are still open; done would require an agreed design plus implementation and coverage for polygon bounds.

Written by the indexing model from the issue text.