Firestore: UpdateData<T> does not properly type nested dynamic keys

### Operating System

Windows 11

### Environment (if applicable)

TypeScript v5

### Firebase SDK Version

12.15.0

### Firebase SDK Product(s)

Firestore

### Project Tooling

Next.js v16 app

### Detailed Problem Description

I have a document that has many nested dynamic fields using the `Record` type (e.g. Record>). When wrapping the type of my document with `UpdateData`, the dynamic field has the type `any` instead of the type `SomeType | FieldValue | undefined`, which is what I had expected given `UpdateData`'s behavior when used on static types.

Additionally, this issue was only observed when the `Record` type was nested in other types and not when it was used at the top-level.

### Steps and code to reproduce issue

**Nested Dynamic Keys are inferred incorrectly**
```
type TestDoc = {
dynamicKeys: Record;
staticKeys: {
staticKey: number;
}
}

type UpdateTestDoc = UpdateData;
```
Type inference on `UpdateTestDoc` gives:
```
type UpdateTestDoc = {
[key: `dynamicKeys.${string}`]: any;
dynamicKeys: { ... 1 more } | FieldValue | undefined;
staticKeys: { ... 1 more } | FieldValue | undefined;
"staticKeys.staticKey": number | FieldValue | undefined;
}
```
The types of static nested fields are inferred properly while the dynamic nested field `dynamicKeys.${string}` is not. It has type `any` when the expected would be `string | FieldValue | undefined`.

**Top-Level Dynamic Keys are inferred properly**
This is only an issue when the dynamic key is nested. If it's top-level, it works fine as shown below:
```
type TestDoc = Record;
type UpdateTestDoc = UpdateData;
```
Type inference on `UpdateTestDoc` gives:
```
type UpdateTestDoc = {
[key: string]: string | FieldValue | undefined;
}
```