psql: Add COMPLETE_WITH_FILES and COMPLETE_WITH_GENERATOR macros.

psql: Add COMPLETE_WITH_FILES and COMPLETE_WITH_GENERATOR macros.

While most tab completions in match_previous_words() use
COMPLETE_WITH* macros to wrap rl_completion_matches(), some direct
calls to rl_completion_matches() still remained.

This commit introduces COMPLETE_WITH_FILES and COMPLETE_WITH_GENERATOR
macros to replace these direct calls, enhancing both code consistency
and readability.

Author: Yugo Nagata <nagata@sraoss.co.jp>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Discussion: https://postgr.es/m/20250605100835.b396f9d656df1018f65a4556@sraoss.co.jp