[FEA] Improve Null-Aware Operator Support in AST-Codegen

[lamarrr]

Description

This pull-request follows-up #19831 and extends support for Null-aware filters and transforms. Addresses #20177

Changeset Summary

• Adds a new null_output policy to inform the transform to not generate null-masks, this is important for null-aware operators that are intended to actually discard null values. null_output::NON_NULLABLE will not generate null-masks for the transform result
• Adds null context to row_ir's nodes to generate code for null-specific contexts
• Adds is_null_aware and is_always_nonullable attributes to row_ir's node's as an optimization to avoid generating bitmasks in the common case.
• Adds a may_evaluate_null attribute to the kernel to signify that a null-mask is not needed for the transform operation
• Moves bitmask computation into the transform kernel, which will reduce computation time for wide tables
• Minor refactoring
• [Pending] Fix null-propagation in filters when null values are selected, i.e., NULL_LOGICAL_AND operators (currently failing test).
• Tests for these changes

Story #18023

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.