Parquet pruning predicate for IS NULL

[houqp]

Describe the bug

col = null expression evaluation throws a runtime error when getting evaluated against statistics array, which resulted in incorrect true result when the stats has null count set to 0.

The other problem is col = null expression is converted into col_min <= NULL AND NULL <= col_max predicate expression. I believe we should be handling null as a special case and return an expression that checks against null count column instead.

To Reproduce

See our test cases at: https://github.com/apache/arrow-datafusion/blob/f027e5f4d9a44ad9cc879c133abc913f78fa76f0/datafusion/src/physical_plan/file_format/parquet.rs#L722-L763

The test case asserts that results for both row groups should return true, while them should both be false instead because both row groups have null count set to 0.

Expected behavior

col = null row group should be evaluated by taking row group null count stats into account.

[alamb]

It should be noted that this is an 'optimization' bug rather than a correctness bug -- in the sense that returning false means "don't filter the row group" and returning true means "do filter (aka skip) the row group"