Investigate partial results for workspace/symbol request

[rgrunber]

https://microsoft.github.io/language-server-protocol/specifications/specification-current/#workspace_symbol seems to support partial results and with changes like #1688 coming eventually, it might be great to have this.

On the JDT-LS side WorkspaceSymbolHandler aggregates the results into a list that is accessible from the callback methods that are triggered for every new match. We don't have to wait for all results.

[rgrunber]

The LSP spec supports this, but it would be good to know which clients do. For example, looking at microsoft/vscode#105870 , there is no support, as the workspace/symbol request currently sends a null partialResultToken.