fix(agg): fix `first_value` and `last_value` to not ignore NULLs #19332

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Fix the behavior of `first_value` and `last_value` in batch aggregate query and both batch & streaming window function query to align with PostgreSQL, so that they don't ignore NULL values. This may be a breaking change if you have streaming jobs containing `first_value`/`last_value` window function calls and there are NULL values before.	Incomplete
#19332 👈	Incomplete
`main`	Incomplete
Nov 12, 11:03 PM EST: Graphite couldn't merge this PR because it failed for an unknown reason (This repository has GitHub's merge queue enabled, which is currently incompatible with Graphite).	Incomplete