Autoclick Tests: Improve UI test stability with string-based locators

Replaced brittle integer resource ID lookups with string-based IDs
for UI elements. This change addresses flakiness caused by resource ID
changes, making tests more robust.

Bug: 418259247
Test: atest AutoclickPanelTests
Flag: com.android.server.accessibility.enable_autoclick_indicator
Change-Id: Id7903378a3fc590d561ff0fe72e7a67ca55539b3