SQL: make foreign tags for 'interenal' functions

[masatake]

CREATE FUNCTION isnlt(ean13, ean13)
        RETURNS boolean
        AS 'int8lt'
        LANGUAGE 'internal'
        IMMUTABLE STRICT
        PARALLEL SAFE;

This change extracts int8lt as a function in the C language.

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 86.01%. Comparing base (c71080d) to head (94a2a2a). :warning: Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4240      +/-   ##
==========================================
+ Coverage   85.98%   86.01%   +0.02%     
==========================================
  Files         249      249              
  Lines       64102    64119      +17     
==========================================
+ Hits        55121    55154      +33     
+ Misses       8981     8965      -16     

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[masatake]

Now we have version information for each kind, role, field, and extra. So the Changes section of the man pages is redundant.