Implement columnar min/max aggregate functions for text

[akuzm]

Currently we only have these functions for arithmetic types, but they are sometimes used for text as well as a tie-breaker.

[codecov]

Codecov Report

❌ Patch coverage is 82.66667% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.45%. Comparing base (f5547ca) to head (3ab4860).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
tsl/src/nodes/vector_agg/function/minmax_text.c	82.66%	0 Missing and 13 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9104      +/-   ##
==========================================
+ Coverage   82.34%   82.45%   +0.10%     
==========================================
  Files         243      244       +1     
  Lines       47822    47921      +99     
  Branches    12196    12229      +33     
==========================================
+ Hits        39377    39511     +134     
- Misses       3582     3592      +10     
+ Partials     4863     4818      -45     

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