Add `uri?: DocumentUri` to DocumentSymbol

[svenefftinge]

The DocumentSymbol data type represents a symbol within a document. So far, the document's uri is implied from the call context.
It would be good to have an optional uri?: DocumentUri field to support usage of the data type in other scenarios, where the document uri cannot be implied from the call:

• outline (including inherited members)
• call hierarchy
• type hierarchy

See also

• Add proposed textDocument/callHierarchy extension vscode-languageserver-node#420
• [WIP] Proposal for type hierarchy vscode-languageserver-node#346 (comment)

[kittaakos]

PR: microsoft/vscode-languageserver-node#425

[dbaeumer]

Closing based on the comments provided in microsoft/vscode-languageserver-node#425