Rerequest completion items when text is deleted/retyped

[waf]

Type "G" to get all completions starting with "G", then backspace and press "H" -- we incorrectly used the cached completions for "G".

Instead, we now detect that the completions don't match and re-invoke the completion callback with the newly typed text.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.7%. Comparing base (9d22b9d) to head (3743622).

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #306   +/-   ##
=====================================
  Coverage   86.7%   86.7%           
=====================================
  Files         48      48           
  Lines       4130    4131    +1     
  Branches     686     685    -1     
=====================================
+ Hits        3582    3583    +1     
  Misses       381     381           
  Partials     167     167           

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