Inconsistent behavior with Generic ElementType

### 🔎 Search Terms

JSX, Generic ElementType, TS2786

### 🕗 Version & Regression Information

- Behavior seen in 5.8.3 and 5.9.0-dev.20250703
- I was unable to test this on prior versions

### ⏯ Playground Link

_No response_

### 💻 Code

```ts
export namespace dsl {
export namespace JSX {
export type Element = {
name: U
type: string
children: Element[]
}

[tsconfig.json](https://github.com/user-attachments/files/21047590/tsconfig.json)

export function createElement(
tag: JSX.ElementType,
props : { name: U },
...children: JSX.Element[]
): JSX.Element {
return tag(props, ...children)
}
}

function Form(props: { name: U }, ...children: dsl.JSX.Element[]) {
return { ...props, type: "form", children }
}

const formDesugared = dsl.createElement(
Form, { name: "one" }
)

const form = (
// <--- Error here, error TS2786: 'Form' cannot be used as a JSX component.
)

```

### 🙁 Actual behavior

Compile error:

sui.tsx:31:6 - error TS2786: 'Form' cannot be used as a JSX component.
Its type '(props: { name: U; }, ...children: Element[]) => { type: string; children: Element[]; name: U; }' is not a valid JSX element type.
Types of parameters 'props' and 'props' are incompatible.
Type '{ name: unknown; }' is not assignable to type '{ name: string; }'.
Types of property 'name' are incompatible.
Type 'unknown' is not assignable to type 'string'.

31

### 🙂 Expected behavior

Changing props: { name: U } in the definition of ElementType to props: { name: string } causes the code to compile [loosing the wanted typing of the resulting Element

Since the desugared version of the code compiles and infers types correctly, I'd expect the JSX code to compile, or at least produce a less deeply mysterious error - the type of the 'name' property plainly *isn't* unknown.

### Additional information about the issue

_No response_

Reproduce the .tsx example with the linked tsconfig.json on TypeScript 5.8.3 and the 5.9 development version, comparing JSX with dsl.createElement and the TS2786 diagnostic. Trace how JSX.ElementType checks the generic Form; done means the JSX form compiles consistently with the desugared call, preserves the intended inferred Element typing, and avoids the misleading unknown-name error.

Written by the indexing model from the issue text.