Make the virtual application shell TypeScript-only

### Prerequisites

- [x] I have written a descriptive issue title
- [x] I have searched existing issues to ensure the feature has not already been requested

### 🚀 Feature Proposal

Currently in `@fastify/vue` and `@fastify/react`, TypeScript support is enabled by offering an alternate virtual application shell, `/virtual-ts`, which is an exact copy of `/virtual` (in the package source) but has TypeScript files instead. In order to support both JS and TS shells, one needs to set the `ts` flag in the respective Vite plugin as well. This can be avoided by simply defaulting to TypeScript for the virtual application shell.

For users who want to customize their application shell, having a TypeScript-first setup is beneficial, because it can be leveraged to illuminate several aspects of the API at the outset, but it can also be easily removed or selectively removed.

This issue tracks work on this change.

### Motivation

_No response_

### Example

_No response_