* adds gopls command line tool for call hierarchy
* adds lsp setup for call hierarchy
* adds handler for textDocument/prepareCallHierarchy to display selected
identifier and get incoming/outgoing calls for it
* setup testing
Change-Id: I0a0904abdbe11273a56162b6e5be93b97ceb9c26
Reviewed-on: https://go-review.googlesource.com/c/tools/+/246521
Run-TryBot: Danish Dua <danishdua@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>