Move basic change state from router to change view model

Release-Notes: skip
Google-Bug-Id: b/247042673
Change-Id: I3c59896837b18709fbc4bb8584d3abb7354492f1

polygerrit-ui/app/models/views/change.ts

diff --git a/polygerrit-ui/app/models/views/change.ts b/polygerrit-ui/app/models/views/change.ts
index 9701b54..3f3c76b 100644
--- a/polygerrit-ui/app/models/views/change.ts
+++ b/polygerrit-ui/app/models/views/change.ts
@@ -200,6 +200,15 @@
   define<ChangeViewModel>('change-view-model');
 
 export class ChangeViewModel extends Model<ChangeViewState | undefined> {
+  public readonly changeNum$ = select(this.state$, state => state?.changeNum);
+
+  public readonly patchNum$ = select(this.state$, state => state?.patchNum);
+
+  public readonly basePatchNum$ = select(
+    this.state$,
+    state => state?.basePatchNum
+  );
+
   public readonly childView$ = select(this.state$, state => state?.childView);
 
   public readonly tab$ = select(this.state$, state => state?.tab);