make client window capabilities optional

[kattouf]

At first, I got an error when trying to use the server with the Zed editor:

error: keyNotFound(CodingKeys(stringValue: "messageActionItem", intValue: nil), Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "params", intValue: nil), CodingKeys(stringValue: "capabilities", intValue: nil), CodingKeys(stringValue: "window", intValue: nil), CodingKeys(stringValue: "showMessage", intValue: nil)], debugDescription: "No value associated with key CodingKeys(stringValue: \"messageActionItem\", intValue: nil) (\"messageActionItem\").", underlyingError: nil))

Then I checked the specification and discovered differences in optionality:

workDoneProgress?: boolean;

https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#serverInitiatedProgress

property path (optional): window.showMessage
messageActionItem?: {
additionalPropertiesSupport?: boolean;

https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#window_showMessageRequest

property path (optional): window.showDocument

https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#window_showDocument

[mattmassicotte]

Argh, sorry about that.

But thanks so much for finding those issues and for correcting them. I really appreciate it!

[mattmassicotte]

(Also don't worry about CI, it's expected it has gone wrong and I'll look into that separately.)