Renamed `RouterFunction.andSame()` to `and()`, and `and()` to
`andOther()`. The reason for this change is that we can expect most
RouterFunctions to be parameterized over ServerResponse, and thus it
makes sense to use the shortest composition method (`and()`) for
composing router functions of the same type.
When a user composes different response types, such as composing a
`RouterFunction<RenderingResponse>` with an
`RouterFunction<EntityResponse<?>`, the `andOther` method is to be used,
but this is a less common scenario.
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