PostgreSQL: Display the index operator class before the sort options

[LucaCappelletti94]

CREATE INDEX ii ON t(c ops DESC) was displayed as CREATE INDEX ii ON t(c DESC ops), putting the operator class after the sort options, which no longer parses as the same index column. PostgreSQL's CREATE INDEX synopsis puts the operator class first, followed by ASC/DESC and NULLS (https://www.postgresql.org/docs/current/sql-createindex.html).

The sort modifiers of OrderByExpr (ASC/DESC, NULLS, WITH FILL) are now written by a shared helper, and IndexColumn prints the column expression, then the operator class, then those modifiers. The parser reads operator classes in every dialect, so the test round-trips CREATE INDEX columns with and without an operator class and sort options in all of them, and checks the parsed operator class and sort order.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.25%. Comparing base (1aabd12) to head (7a1eeb7).

Files with missing lines	Patch %	Lines
src/ast/ddl.rs	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2663   +/-   ##
=======================================
  Coverage   81.25%   81.25%           
=======================================
  Files          42       42           
  Lines       33910    33913    +3     
  Branches    33910    33913    +3     
=======================================
+ Hits        27553    27556    +3     
  Misses       2792     2792           
  Partials     3565     3565           

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