Suggestion: Namespace suggestions

[yucombinator]

I created a proof of concept that uses hhvm --search and Code Actions to provide a (rudimentary) namespace suggestions for unresolved symbols.

Demo here: https://imgur.com/S9zeQue

How it works:

• Every time we see a Unbound error (error code 2049) we take the code producing the error and pass it to hh_client --search which gives us a list of matches

• Each of the match is added to the list of quickfix actions, and shows up when the user hovers over the error in the IDE

• Clicking on one of the quick fix actions will append the namespace before the term.

Ideally this functionality can be added to hh_client LSP server and potentially used for autocompletion. I can clean this up and make a PR but the code behind the demo can be find in its WIP here.

cc: @Wilfred