Add removed BufferedHistoricLayerCoverage.contains method

pageserver/src/tenant/layer_map/historic_layer_coverage.rs

@@ -431,6 +431,14 @@ impl<Value: Clone> BufferedHistoricLayerCoverage<Value> {
         }
     }
 
+    pub fn contains(&self, layer_key: &LayerKey) -> bool {
+        match self.buffer.get(layer_key) {
+            Some(None) => false,                         // layer remove was buffered
+            Some(_) => true,                             // layer insert was buffered
+            None => self.layers.contains_key(layer_key), // no buffered ops for this layer
+        }
+    }
+
     pub fn insert(&mut self, layer_key: LayerKey, value: Value) {
         self.buffer.insert(layer_key, Some(value));
     }