Improve Percy stability by better scoping snapshots (#10207)

cypress/support/percy.ts

@@ -22,6 +22,7 @@ declare global {
     namespace Cypress {
         interface SnapshotOptions extends PercySnapshotOptions {
             domTransformation?: (documentClone: Document) => void;
+            allowSpinners?: boolean;
         }
 
         interface Chainable {
@@ -38,6 +39,10 @@ declare global {
 }
 
 Cypress.Commands.add("percySnapshotElement", { prevSubject: "element" }, (subject, name, options) => {
+    if (!options?.allowSpinners) {
+        // Await spinners to vanish
+        cy.get(".mx_Spinner").should("not.exist");
+    }
     cy.percySnapshot(name, {
         domTransformation: (documentClone) => scope(documentClone, subject.selector),
         ...options,