PostgreSQL: Parse schema-qualified keyword function calls

[LucaCappelletti94]

The parser rejects SELECT public.floor(3) and SELECT pg_catalog.floor(3) because the suffix fallback consumes the keyword as an identifier. Qualified keyword names require ordinary function-call parsing with their full names preserved, consistent with PostgreSQL's function resolution rules.

Bare FLOOR(3) and keyword column references such as t.interval retain their expression forms.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.31%. Comparing base (d32825d) to head (2d90049).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2685      +/-   ##
==========================================
+ Coverage   81.29%   81.31%   +0.01%     
==========================================
  Files          42       42              
  Lines       33950    33953       +3     
  Branches    33950    33953       +3     
==========================================
+ Hits        27601    27608       +7     
+ Misses       2785     2782       -3     
+ Partials     3564     3563       -1     

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