Support resolving completion items about lsp HOT 2 CLOSED

We may be able to resolve and update completions async if the list of completions is not too long.
Another option:

1. Detect when a completion has been committed: https://forum.sublimetext.com/t/how-to-detect-commands-run-by-a-plugin-when-an-autocomplete-entry-is-clicked-on-by-the-mouse/19073/2
2. Resolve completion item to get snippet
3. Replace inserted text with a snippet (https://forum.sublimetext.com/t/how-to-insert-a-snippet-from-a-plugin/3651)

from lsp.

Support for resolving completions merged in #92, can look at resolving completions earlier in the future.

from lsp.