Make `ServerOperationRegistryGenerator` protocol-agnostic (#1525)

`ServerOperationRegistryGenerator` is the only server generator that is
currently not protocol-agnostic, in the sense that it is the only
generator that contains protocol-specific logic, as opposed to
delegating to the `Protocol` interface like other generators do.

With this change, we should be good to implement a
`RustCodegenDecorator` loaded from the classpath that implements support
for any protocol, provided the decorator provides a class implementing
the `Protocol` interface.

This commit also contains some style changes that are making `ktlint`
fail. It seems like our `ktlint` config was recently broken and some
style violations slipped through the cracks in previous commits that
touched these files.