Missing reference when using a symbol from a submodule

[dhanak]

In addition to the numerous "missing reference" issues (#988, #1204, #1230, #1232, #1276), I noticed that I get missing reference issues when I try to import symbols from a submodule of a toplevel module. E.g.:

using Base.Threads: threadid # threadid gets a missing reference warning
using Base.Threads: @spawn   # oddly enough, @spawn does not

using MyModule.Submodule: my_function # both Submodule and my_function get missing reference warnings

Quite annoying, because I often use small scripts to inspect and test the interior state of my packages, and LS doesn't really appreciate this.