Remove Oracle ROWNUM from SQLServer unparenthesized functions

[thswlsqls]

Fixes #39100.

Changes proposed in this pull request:

• Remove ROWNUM, ROWNUM_ and ROW_NUMBER from SQLServerFunctionOption.getUnparenthesizedFunctionNames(); these are Oracle pseudo-columns that SQL Server does not have (ROW_NUMBER always needs () + OVER).
• Resolve the existing maintainer TODO that already asked to remove these three names.
• The set is consumed by ColumnSegmentBinder.isUnparenthesizedFunction(), which skipped binding for any identifier in it; a real SQL Server column named ROWNUM was therefore left unbound (wrong output).
• Restore parity with the sibling dialects: among all dialect FunctionOptions only Oracle legitimately keeps these pseudo-columns; SQLServer was an Oracle copy remnant.
• Update SQLServerFunctionOptionTest to assert the remaining niladic functions stay and the three Oracle names are gone.

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[terrymanu]

Please resolve conflict first