Rename `ServerHttpProtocolGenerator` to `ServerHttpBoundProtocolGenerator` (#1251)

And `ServerHttpProtocolImplGenerator` to
`ServerHttpBoundProtocolTraitImplGenerator`.

The client-side classes are named `HttpBoundProtocolGenerator` and
`HttpBoundProtocolTraitImplGenerator`, so the server-side clases should
just add the "Server" prefix and not deviate from the naming convention.