Update unit test once upstream merges (windows using aggregates)

[timsaucer]

Describe the bug

Once apache/datafusion#12009 from upstream reaches this repository, which should be DataFusion 42, update the unit tests test_window_functions for first_value and last_value

To Reproduce

Try to use the first_value and last_value functions as window functions in the unit tests.

Expected behavior

Tests should pass

Additional context

[timsaucer]

Also update online documentation

[timsaucer]

Closed by #871