Fix missing reference action only work if package have been `using`d

[fredrikekre]

Probably an issue in SymbolServer or StaticLint, but e.g. in

import Example
hello("foo")              # Missing reference hello

this can't be fixed because Example isn't in https://github.com/julia-vscode/LanguageServer.jl/blob/018d838372837bdc4519e37cc7c4bab10527fc82/src/requests/actions.jl#L292

In contrast,

using Example
some_non_exported_function(..)

works.