[ts-next-plugin] test: add metadata warn no type test (#78505)
### Why?
This PR initiates the migration of manual testing of the Next.js TypeScript plugin to an automated language service plugin test. It replaced the existing metadata `missing-type-warning` fixture with the `warn-no-type` test (naming for consistency, such as future `error-on-client`).
### Testing Plan
This PR adds the tests and fixtures for the metadata plugin to **warn when no type is provided** for metadata config exports (`metadata` and `generateMetadata`).
1. The fixtures are tested into two categories: 1) "**has type**": expects no warning, and 2) "**no type**": expects a warning.
2. For "has type", the types are from `next` or custom.
3. Each section consists of inline exports and separate exports (`export { ... }`).
4. For the fixtures of `generateMetadata`, it is divided into a function, an arrow function, and a function expression divided with sync and async.
<details><summary>Structure Details</summary>
<p>
#### `metadata`
```
.
├── has-type/
│ ├── export-inline/
│ │ ├── from-next
│ │ └── from-others
│ └── export-separate/
│ ├── from-next
│ └── from-others
└── no-type/
├── export-inline
└── export-separate
```
#### `gerenateMetadata`
```
.
├── has-type/
│ ├── export-inline/
│ │ ├── from-next/
│ │ │ ├── async/
│ │ │ │ ├── arrow-function
│ │ │ │ ├── function-declaration
│ │ │ │ └── function-expression
│ │ │ └── sync/
│ │ │ ├── arrow-function
│ │ │ ├── function-declaration
│ │ │ └── function-expression
│ │ └── from-others/
│ │ ├── async/
│ │ │ └── ...
│ │ └── sync/
│ │ └── ...
│ └── export-separate/
│ ├── from-next/
│ │ ├── async/
│ │ │ └── ...
│ │ └── sync/
│ │ └── ...
│ └── from-others/
│ ├── async/
│ │ └── ...
│ └── sync/
│ └── ...
└── no-type/
├── export-inline/
│ ├── async/
│ │ └── ...
│ └── sync/
│ └── ...
└── export-separate/
├── async/
│ └── ...
└── sync/
└── ...
```
</p>
</details>
### Follow Up
The metadata currently has one more feature: an error when using metadata exports within Client Components.
