Use new API for textDocument/documentSymbol

[bizzyman]

Hi,

Since VScode 1.25's new outline feature (see https://github.com/redhat-developer/vscode-java/issues/586), the LSP spec has been updated (https://microsoft.github.io/language-server-protocol/specification#textDocument_documentSymbol) with new features, the most important one being the children? field, which allows for a hierarchical outline to be created from the symbols returned, will javascript-typescript-langserver be implementing this new spec?

[AArnott]

I need this as well, mostly for the new range vs. selectionRange fields.