Use single accumulating shell transition handler mapping

Bug: 323356094
Test: adb shell -t perfetto \
     -c - --txt \
     -o /data/misc/perfetto-traces/trace \
   <<EOF
   unique_session_name: "transitions_tracing"
   buffers: {
       size_kb: 63488
       fill_policy: RING_BUFFER
   }
   data_sources: {
       config {
           name: "com.android.wm.shell.transition"
       }
   }
   duration_ms: 10000
EOF

Change-Id: I6f645a7b5864ca81dbf6c5bf4d58634746e980aa