[cache (rust)] Add Mapping::is_dirty()

src/cache/mapping.rs

@@ -24,6 +24,10 @@ impl Mapping {
     pub fn is_valid(&self) -> bool {
         return (self.flags & MappingFlags::Valid as u32) != 0;
     }
+
+    pub fn is_dirty(&self) -> bool {
+        return (self.flags & MappingFlags::Dirty as u32) != 0;
+    }
 }