Function reconstruct 

pub fn reconstruct(
    ours_regions: &[FileRegion],
    theirs_regions: &[FileRegion],
    theirs_entities: &[SemanticEntity],
    ours_entity_map: &HashMap<&str, &SemanticEntity>,
    resolved_entities: &HashMap<String, ResolvedEntity>,
    merged_interstitials: &HashMap<String, String>,
    marker_format: &MarkerFormat,
) -> String

Reconstruct a merged file from resolved entities and merged interstitials.

Uses “ours” region ordering as the skeleton. Inserts theirs-only additions at their relative position (after the entity that precedes them in theirs).