vue-server-renderer type definitions

[cdekok]

What problem does this feature solve?

Using vue-server-renderer with typescript, it seems vue and vue-router are supported it would be nice if vue-server-renderer came with typings to.

What does the proposed API look like?

The same but with types directory.

[yyx990803]

@ktsn would you be interested in working on this? The API surface is not too big so it should be relatively straightforward.

[ktsn]

@yyx990803 Done! #5775