SystemUI: Add flag to not use runBlocking

- As seen in the past, runBlocking is very problematic and should
  never be used in SystemUI. This flag allows switching to an
  alternate method used as appropriate, without use of runBlocking

Bug: 411091082
Flag: com.android.systemui.do_not_use_run_blocking
Change-Id: I57f949b4b7fcdc3836b0200d58f5ed18d6fe503d