Completions Rework after Hierarchical Namespaces #1252
Description
As they're currently implemented, completions make a lot of assumptions. They only check the global scope for whether or not they need to add an open statement, and they take some short cuts with respect to re-triggering completion. Additionally, they don't actually query the resolver for what is in scope at a given point.
Completions will have to be generally re-worked after hierarchical namespaces go in. We will prefer import to open, and completions will have to understand that, e.g., Diagnostics is a sub-namespace of Quantum, which is a sub-namespace of Microsoft.
related: #493