Literal expression validation does not match documentation

Nobody has claimed this yet.

The style spec documentation for [literal expressions](https://docs.mapbox.com/mapbox-gl-js/style-spec/expressions/#types-literal) says it requires an array or object in the second argument. However, in Studio, an expression like the one below passes validation.

`
[ "literal", "#333333" ]
`

**mapbox-gl-js version**: `@mapbox/mapbox-gl-style-spec@13.11.0`

**browser**: N/A

### Steps to Trigger Behavior

Save this style, upload to Studio, and try clicking on the single layer.

```
{
"layers": [
{
"id": "this-be-the-problem",
"layout": {},
"paint": {
"fill-extrusion-color": [
"case",
[
"boolean",
false
],
"#333333",
[
"literal",
"#999999"
]
]
},
"source": "composite",
"source-layer": "building",
"type": "fill-extrusion"
}
],
"name": "Problematic Literal",
"sources": {
"composite": {
"type": "vector",
"url": "mapbox://mapbox.mapbox-streets-v8"
}
},
"version": 8
}
```

I'm sorry I don't have a better way to illustrate this, but Studio uses validator functions when you try uploading any style.

This causes issues in our json editor, which enforces Studio limitations around object literals and only allows arrays in `literal` expressions.

I'm not sure how long this behavior has been around, but it's likely that stricting up this validation could break production styles. It would be worth seeing how many styles this would affect, cc @samanpwbb.

Start with the style spec documentation for literal expressions and the validator functions used when Studio uploads a style. Compare the documented array-or-object requirement with the accepted string expression and investigate whether existing production styles depend on that behavior. Done means the validation behavior and documentation agree without overlooking the reported editor impact.

Written by the indexing model from the issue text.