Add import field to metadata to satisfy older versions (#11797)

Fixes #11742

I was [wrong](#11742 (comment)) - not the _new_ fields make metadata broken for older versions, but removing an _old_ field.

This PR bring it back, which solves the issue - for a while.

app/ydoc-server/src/edits.ts

@@ -74,7 +74,11 @@ export function applyDocumentUpdates(
   if (codeChanged || idsChanged || metadataChanged) {
     // Update the metadata object.
     // Depth-first key order keeps diffs small.
-    newMetadata = { node: {}, widget: {} }
+    newMetadata = {
+      node: {},
+      widget: {},
+      import: {}, // "import" is required by older versions (even though they don't use it)
+    }
     root.visitRecursive(ast => {
       let pos = ast.nodeMetadata.get('position')
       const vis = ast.nodeMetadata.get('visualization')

app/ydoc-server/src/languageServerSession.ts

@@ -350,7 +350,7 @@ class ModulePersistence extends ObservableV2<{ removed: () => void }> {
       // @ts-expect-error This is SAFE. `this.state` is only `readonly` to ensure that
       // this is the only place where it is mutated.
       this.state = state
-      if (state === LsSyncState.Synchronized) this.trySyncRemoveUpdates()
+      if (state === LsSyncState.Synchronized) this.trySyncRemoteUpdates()
     } else {
       throw new Error('LsSync disposed')
     }
@@ -450,10 +450,10 @@ class ModulePersistence extends ObservableV2<{ removed: () => void }> {
     } else {
       this.updateToApply = update
     }
-    this.trySyncRemoveUpdates()
+    this.trySyncRemoteUpdates()
   }
 
-  trySyncRemoveUpdates() {
+  trySyncRemoteUpdates() {
     if (this.updateToApply == null) return
     // apply updates to the ls-representation doc if we are already in sync with the LS.
     if (!this.inState(LsSyncState.Synchronized)) return