Fix RegistrationOptions encoding to correctly merge objects

[Steffeeen]

The two members of the different RegistrationOptions should be encoded into a single object which contains the members of each of the two members. This accidentally broke in 7530abc.

By not merging the two objects, the encoding ended up like this:

"registerOptions": {
    "signatureHelpOptions": {
        "triggerCharacters": [
            "(",
            "["
        ],
        "retriggerCharacters": [
            ",",
            ":"
        ]
    },
    "textDocumentRegistrationOptions": {
        "documentSelector": [
            {
                "language": "swift"
            }
        ]
    }
}

while it should look like this:

"registerOptions": {
    "documentSelector": [
        {
            "language": "swift"
        }
    ],
    "triggerCharacters": [
        "(",
        "["
    ],
    "retriggerCharacters": [
        ",",
        ":"
    ]
}

This subsequently lead to the capabilities not being registered on the language server client, which leads to for example semantic tokens not working in VSCode.

The changes in LSPAny+Coding.swift are needed to ensure that we don't hit the precondition in the willset {} of storage.

[ahoppen]

Thanks a lot for noticing and tracking this down 🙏🏽

[rintaro]

Thank you!

[rintaro]

@Steffeeen Could you open a PR for release/6.4.x branch? 🙏