Add support for textDocument/diagnostic, workspace/diagnostic (3.17)

[ebkalderon]

Added

• Add support for textDocument/diagnostic request (link).
• Add support for workspace/diagnostic request (link).
• Add support for workspace/diagnostic/refresh request (link).

Changed

• Change url_map() to be generic over the HashMap value type, making this code reusable in textDocument/diagnostic.
• Add diagnostic field to WorkspaceClientCapabilities struct.
• Add diagnostic field to TextDocumentClientCapabilities struct.
• Add diagnostic_provider field to ServerCapabilities struct.

It turns out these new 3.17.0 requests were unfortunately missed in PR #255.

[flyingmutant]

@Marwes sorry for the ping, can you please take a look? This is an unfortunate omission in the 3.17 support. Thanks a lot for all your work on lsp-types!

[Marwes]

Looks good! Released as 0.94.1.