Allow to mix different collations

Why it matters

This feature solves the limitation of having to use a single collation for a column across all window functions. It enables users to apply different collations to the same column in separate window function clauses, providing greater flexibility in text comparison and sorting within queries.

How to use it

Simply specify different collations explicitly in the window function definitions when using the same column. ClickHouse will apply the respective collations independently for each window function.