[Follow-up #23696] Extract generic empty-row-group stripping from strip_empty_row_groups #24287

Follow-up to #23696 (review comment).

strip_empty_row_groups in datafusion/datasource-parquet/src/access_plan.rs currently couples the generic empty-row-group stripping (dropping row groups whose RowSelection is empty after page-index pruning) with this PR's fully_matched tracking. The empty-RG stripping itself is broadly useful and applies independently of fully_matched, so it could be extracted into its own PR.

Suggested by @adriangb in #23696 (comment)