Fix dumping shell transition handler mapping onFlush

Because the tls state is per tracing instance and per thread, and the onFlush callback runs on a different thread than the tracing function, we ended up with a new TLS state onFlush which contained an empty map.

Test: atest FlickerLibTest:android.tools.common.flicker.config.QuickswitchTest#canExtractQuickswitch
Bug: 323159148
Change-Id: I0d1338b9c3831d3be4981e19e1f95769afc2a664