[BaseTransientBottomBar] Check for nullable AccessibilityService

Resolves #1885
Resolves #1888

GIT_ORIGIN_REV_ID=35572a920b4bdd66e416d428c55416df7c498db6
PiperOrigin-RevId: 343873267

(cherry picked from commit 2b95793)

Author: matpag

lib/java/com/google/android/material/snackbar/BaseTransientBottomBar.java

@@ -1098,6 +1098,9 @@ void onViewHidden(int event) {
 
   /** Returns true if we should animate the Snackbar view in/out. */
   boolean shouldAnimate() {
+    if (accessibilityManager == null) {
+      return true;
+    }
     int feedbackFlags = AccessibilityServiceInfo.FEEDBACK_SPOKEN;
     List<AccessibilityServiceInfo> serviceList =
         accessibilityManager.getEnabledAccessibilityServiceList(feedbackFlags);