Fix inlay map tests

Co-Authored-By: Antonio Scandurra <antonio@zed.dev>

crates/editor/src/multi_buffer/anchor.rs

@@ -85,6 +85,24 @@ impl Anchor {
     {
         snapshot.summary_for_anchor(self)
     }
+
+    pub fn is_valid(&self, snapshot: &MultiBufferSnapshot) -> bool {
+        if *self == Anchor::min() || *self == Anchor::max() {
+            true
+        } else if let Some(excerpt) = snapshot.excerpt(self.excerpt_id) {
+            self.text_anchor.is_valid(&excerpt.buffer)
+                && self
+                    .text_anchor
+                    .cmp(&excerpt.range.context.start, &excerpt.buffer)
+                    .is_ge()
+                && self
+                    .text_anchor
+                    .cmp(&excerpt.range.context.end, &excerpt.buffer)
+                    .is_le()
+        } else {
+            false
+        }
+    }
 }
 
 impl ToOffset for Anchor {