feat(core): first class a11y support (#8909)

packages/core/accessibility/accessibility-service-common.ts

@@ -0,0 +1,35 @@
+import { Observable } from '../data/observable';
+
+export class SharedA11YObservable extends Observable {
+	accessibilityServiceEnabled?: boolean;
+}
+
+export const AccessibilityServiceEnabledPropName = 'accessibilityServiceEnabled';
+
+export class CommonA11YServiceEnabledObservable extends SharedA11YObservable {
+	constructor(sharedA11YObservable: SharedA11YObservable) {
+		super();
+
+		const ref = new WeakRef(this);
+		let lastValue: boolean;
+
+		function callback() {
+			const self = ref?.get();
+			if (!self) {
+				sharedA11YObservable.off(Observable.propertyChangeEvent, callback);
+
+				return;
+			}
+
+			const newValue = !!sharedA11YObservable.accessibilityServiceEnabled;
+			if (newValue !== lastValue) {
+				self.set(AccessibilityServiceEnabledPropName, newValue);
+				lastValue = newValue;
+			}
+		}
+
+		sharedA11YObservable.on(Observable.propertyChangeEvent, callback);
+
+		this.set(AccessibilityServiceEnabledPropName, !!sharedA11YObservable.accessibilityServiceEnabled);
+	}
+}