[automerge] Write default accessibility service only when user enter into...

[automerge] Write default accessibility service only when user enter into corresponding page. 2p: 2f2f0e98 2p: e1e4a674

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Settings/+/17655026

Change-Id: I53be724a2717e6d3c5ee74859e3b6d761d348fa7