Opening a reference document sends a `textDocument/didClose` notification to LSP instead of `textDocument/didOpen`

[ahoppen]

When opening a URL scheme whose content is provided by a workspace/getReferenceDocument request from SourceKit-LSP, VS Code will send a textDocument/didClose request to SourceKit-LSP instead of a textDocument/didOpen. Closing the document sends another textDocument/didClose notification.

Steps to reproduce:

• Build SourceKit-LSP with Support semantic functionality in generated interfaces if the client supports getReferenceDocument sourcekit-lsp#1887 and set it as the SourceKit-LSP server path
• Apply Only change scheme of .swiftinterface files to readonly if old scheme was file #1276 to the vscode-swift sources
• Jump to definition on any import statement
• Notice that VS Code sends a textDocument/didClose notification to SourceKit-LSP when the document is actually being opened.

[ahoppen]

This no longer reproduces after updating my vscode-swift checkout.