BUG DECODING KEYS FROM FIRESTORE.

### Description

The firestore decoder keep in mind _JSONStringDictionaryDecodableMarker.Type. So for maps, if we have something like this:

``
{
"name": {"KEY": VALUE }
}
``

and we decode it with a codable structure with a property of type `[String: String]` it works.

The Behavior using `[EnumStringRawValue: String]` does fail into:
```
typeMismatch : 2 elements
- .0 : Swift.Array
▿ .1 : Context
▿ codingPath : 1 element
- 0 : CodingKeys(stringValue: "KEY", intValue: nil)
- debugDescription : "Expected to decode Array but found a dictionary instead."
- underlyingError : nil
```
Because in this case key is always represented as a String
```
extension Dictionary : _JSONStringDictionaryDecodableMarker where Key == String, Value: Decodable {
static var elementType: Decodable.Type { return Value.self }
}
```

The expected behavior is to decode a map with an enum string raw representable if it can fit on the string raw representable cases.

### Reproducing the issue

Add a document with a map in Firestore.

Try to decode it with document.data() passing as an argument your struct or class metatype. Inside of the struct or class metatype define a map with StringRawValueEnum as key.

### Firebase SDK Version

10.23.0

### Xcode Version

15.2

### Installation Method

Swift Package Manager

### Firebase Product(s)

Firestore

### Targeted Platforms

iOS

### Relevant Log Output

_No response_

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