Tighten Phoenix code completion scope

[cartermak]

Checked for duplicates

No - I haven't checked

Alternatives considered

No - I haven't considered

Related problems

The Phoenix code completion options sometimes include options that don't make sense in the current context.

For example, when writing a directive at the beginning of a sequence, I would expect starting with @ to limit my code completion options to only directives, but I'm still offered command stems that include whatever I've typed after @. This means that, when filling out @IMMEDIATE, I also get code completion offered for flight software command stems that include "IMMEDIATE".

If I type "IMMEDIATE" entirely, the directive disappears from the code completion list. This means that, when I hit "Enter", I end up selecting the first code completion option, which has now become the first flight software command stem to include "IMMEDIATE".

Describe the feature request

The code completion would ideally be better scoped to the current context. It already does this in some ways (e.g., when I have the @HARDWARE directive and start typing on a new line, I get hardware command stems), but there are a lot of scenarios where the code completion offers inappropriate suggestions based on the context.