system server: configure 4 MB perfetto shmem buffer

Increase Perfetto's shmem buffer from default size (256 KB) to 4 MB
to avoid crashes (too long perfetto producer stalls) caused by shmem
chunks exhaustion/contention.

Bug: b/382369925
Flag: android.tracing.system_server_large_perfetto_shmem_buffer
Test: presubmit
Change-Id: I5b6ab40cb3987a7aed7bb09801f02bea3f3962a2