Add Support For `completionItem/resolve`

[Mazyod]

Describe the Bug

Support for completionItem/resolve seems to be missing, since when I send such message to Pyrefly, it fails with the message below.

The significance of support for this method is that it is sent whenever a completion item is selected in the Monaco editor, and it expects the completion item resolved label to be sent back to complete the request. As per the docs, it also allows for optimization on the LSP level for loading the docs and other expensive operations preemptively.

2025-11-26 07:56:43,061 - ERROR - Server - stderr: Handling non-canceled request textDocument/semanticTokens/full (31)
2025-11-26 07:56:43,065 | INFO -    11 ms -      127.0.0.1:60159 - 200 POST /ai/chips/ui/v1/lsp/session/37df84a5/semantictokens
2025-11-26 07:56:43,065 - INFO  - 
2025-11-26 07:56:43,116 - ERROR - Server - stderr: Handling non-canceled request textDocument/diagnostic (32)
2025-11-26 07:56:43,116 | INFO -     3 ms -      127.0.0.1:60159 - 200 POST /ai/chips/ui/v1/lsp/session/37df84a5/diagnostics
2025-11-26 07:56:43,116 - INFO  - 
2025-11-26 07:56:44,042 - ERROR - Server - stderr: Handling non-canceled request textDocument/completion (33)
2025-11-26 07:56:44,043 | INFO -     9 ms -      127.0.0.1:60159 - 200 POST /ai/chips/ui/v1/lsp/session/37df84a5/completion
2025-11-26 07:56:44,043 - INFO  - 
2025-11-26 07:56:44,053 - ERROR - Server - stderr: Handling non-canceled request completionItem/resolve (34)
2025-11-26 07:56:44,053 - ERROR - Server - stderr: Unhandled request: Request { id: RequestId(I32(34)), method: "completionItem/resolve", params: Object {"detail": String("..."), "kind": Number(2), "label": String("input_config"), "sortText": String("0")}

Sandbox Link

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(Only applicable for extension issues) IDE Information

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[grievejia]

Relevant discussion: #1668 (reply in thread)