Feature Request: Layers having state like Features' Feature-State

Nobody has claimed this yet.

## Motivation
Oftentimes when working on Maps with multiple layers I have a need to "dim" or otherwise change a whole layer's paint/layout property dynamically based on user interaction. This is handled by manually calling `setLayout/setPaintProperty`

## Design Alternatives

N/A

## Design
It would be very nice to have a "Layer-State" that works like Feature-State but applied to the whole layer rather than one Feature. This would enable people to build Expressions that change a whole Layer's style with just a call to something like `setLayerState()`.
Another super common use case for this would be toggling a layer on or off with the Visible Layout property.
While it may seem like this design is just exchanging function calls for different functions calls, there are times when I need to change multiple Layout/Paint properties at once to achieve the proper visual effect, and building those changes as Expressions and then simply calling `setLayerState()`. Also, I think this would be a cleaner approach than manually changing the Layout/Paint values in general by making the interaction more state driven rather than effect driven.

### Mock-Up

```
//Add Layer
map.addLayer({
id: "countries",
type: "fill",
source: "country-source",
layout: {
"visibility": [
"case",
["boolean", ["layer-state", "visible"], false],
"visible",
"hidden",
],
},
});

//Toggle Layer off
map.setLayerState("countries", {visible: false});

//Toggle Layer on
map.setLayerState("countries, {visible: true});
```

### Concepts

Same as Feature-State, but for Layers.

### Implementation
I am unfamiliar with the internals of Mapbox.gl, so I am not sure of what the implementation would look like. But if someone were to point me to the best place to start I could definitely take a shot at implementing it.

Start by reading the existing Feature-State behavior and how layer layout and paint properties are currently changed. Define the scope of a layer-wide state API, including expression access and visibility toggling, then determine how completion would be tested against the proposed setLayerState() usage.

Written by the indexing model from the issue text.