x/tools/gopls: support autocompletion of unimported packages

[stamblerre]

See for microsoft/vscode-go#2484 for context.

[ramya-rao-a]

When this does get into gopls please send a PR or log an issue to the vscode Go plugin so that we can disable the similar feature (in non module mode) there to avoid duplicate suggestions

[zchee]

@stamblerre
Just a question.
Is this issue means only of stdlib like gocode?
Or, all of packages ingo.mod?

[stamblerre]

It would be all available packages, not just stdlib.

[zchee]

@stamblerre
great.

Are you doing now develop this feature?
I do not know what you remember to me, but I maintained nsf/gocode for a while. If you not yet develop this feature, I would want to help you.

[stamblerre]

I am not actively working on it yet, so you're absolutely welcome to get started on it.

[jackielii]

@stamblerre @saibing I found out that this is a difference between https://github.com/saibing/tools & https://github.com/golang/tools/tree/ : saibing/tools already have this feature:

screenshot from saibing/tools + coc.nvim + neovim nightly build

[stamblerre]

From microsoft/vscode-go#2575:

There are really two components to this issue. For example (in both cases, time is not imported):

1. Typing "ti<>" and getting package time as part of the autocompletion results.
2. Typing "time.<>" and getting autocompletions for the members of package time.