Show method signature when writing the arguments of the method

[amol-mandhane]

When writing the arguments of the method, textDocument/hover method doesn't apply and there's no documentation available. However, textDocument/signatureHelp is meant exactly for this use-case. LSP client should show the signature when writing the arguments.

signatureHelp method: https://github.com/Microsoft/language-server-protocol/blob/master/protocol.md#textDocument_signatureHelp

[amol-mandhane]

I have a local change for this. If the idea sounds okay, I can send a pull request.

[vibhavp]

Sure, thanks. I'll add a few customize options to your PR and make it work with SignatureHelpRegistrationOptions.triggerCharacters, if it isn't already using it.

[tam5]

What is the status of this, it doesn't seem to work as far as I can tell, but it looks like there is already some code in. Any clues towards the next step?

[yyoncho]

I believe that it does not work the the optimal way. If I recall correctly you should select hover or signature but I believe that the decision should be made by the signature trigger characters that are in initialization options.

[yyoncho]

@tam5 PR at #544