Bad autocomplete behavior

There are a few issues in this .gif.

1. As I start to type 'my' I would expect autocomplete to suggest the local variables above as autocompletions.
2. Once I type `myMap` and hit `.`, autocomplete results come up for `myMap`. Once I backspace, these autocomplete suggestions should go away.
3. As I start typing something new, the stale autocomplete results from `myMap` are still showing up when they shouldn't be.

@elliette @polina-c

Start by reproducing the three autocomplete cases described in the issue and compare them with the attached GIF. Trace the autocomplete implementation responsible for local-variable suggestions and result invalidation; done means local variables are suggested and stale results disappear after backspacing or starting new input.

Written by the indexing model from the issue text.