Rename @hmr module for TypeScript tooling compatibility

[bates64]

Is your feature request related to a problem? Please describe.
TypeScript editor tools complain that they Cannot find module '@hmr'.:

Describe the solution you'd like
Move or alias @hmr to vite/hmr. Then, typings can be provided from the vite package itself.

import { hot } from 'vite/hmr'

// TypeScript knows what `hot` is now!

Describe alternatives you've considered
Users can declare the @hmr module themselves in a .d.ts file:

declare module '@hmr' {
	export const hot: {
		// accept, dispose, on, etc.
	}
}

This requires duplicating type information already available in client.ts and breaks projects if the hmr API changes.

Additional context
It may also be worth allowing __DEV__ to be imported from a module such as vite/env. This would also free TypeScript users from having to declare a global boolean in a declaration file.

[yyx990803]

closed via eab49a4