completions: disable completions when dot-prefix type is unknown

[aviatesk]

Previously, dot-prefixed completions like xarg.x would show irrelevant
global completions when the prefix type could not be resolved.
For now, let's just disable completions entirely in such cases, to
provide a cleaner user experience by not showing unrelated suggestions.

Property completions for non-module values may be added in the future.

Fixes #389

[topolarity]

Thanks for the fix!

when the prefix type could not be resolved

Out of curiosity, when can the prefix type be resolved?

I haven't been able to find any case that JETLS was able to tell me the fields of a local variable or argument yet.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.53%. Comparing base (5b5a6f3) to head (1a8caa2).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #395      +/-   ##
==========================================
+ Coverage   65.51%   65.53%   +0.02%     
==========================================
  Files          44       44              
  Lines        4944     4947       +3     
==========================================
+ Hits         3239     3242       +3     
  Misses       1705     1705              

Flag	Coverage Δ
JETLS.jl	65.53% <100.00%> (+0.02%)	⬆️

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[aviatesk]

Out of curiosity, when can the prefix type be resolved?

The current implementation of resolve_type is quite limited and incorrect, as it only performs abstract interpretation for dot-prefixed expressions in global scope, so it can derive types only when the dot-prefixed object is a global constant.

However, by utilizing the ASTTypeAnnotator added in #227, it would become possible to perform type analysis including local variables.