* Fix return value of LSP shutdown
It is specified as a request that returns null. Returning void causes
the language server to crash.
* Fix empty responses of LSP textDocument/definition
It is specified to return either a Location, an array of Locations, or
null. Hovers are unrelated.
* Fix responses of LSP textDocument/hover
It is specified to either return Hover or null. Psalm could previously
return a success response containing a MarkedString, but with a null
value. MarkedString is not allowed to contain null.
* Implement signature help - closes#1841
* Add explicit signature count
* [LSP] Do analysis for every signatureHelp request
See here: https://github.com/vimeo/psalm/pull/1862#issuecomment-507007346
* Don’t language server information when checking property for init
* Fix signature help for functions
* Add try-catch around signature help Functions::getStorage()
Language Server
---------------
When typing quickly, the LSP client can send multiple messages
in a group, including didChange messages followed by completion
messages. Currently, LanguageServer::doAnalysis() is only called
after a message group is processed. This can result in completion
being done with outdated file contents for example:
Message group with two messages is received
1. `didChange`: file analysis is queued for modified file
2. `completion`: completion attempted on stale file contents
3. `messageGroupRead`: analysis is done, but too late for completion
This commit ensures that any queued file analyses are done prior
to serving completion requests.
