GpuStats: send GpuStats at activity launch hint

USAP preloads the driver in usap pool, and those processes in the pool
are not bound with any applications. Previously we send GpuStats based
on the completion of driver loading. So with usap enabled, we won't be
able to receive stats for system built-in driver.

If we send the stats when all the existing stats fields are filled,
there will be tons of selinux violations, because those non app
processes are trying to send the stats as well.

So we end up sending the stats based on the hint of activity launch.

Bug: 131866357
Test: dumpsys gpu with enable/disable usap and check the selinux
Change-Id: Ib1291f3bb82d4cd1c1a893d8ea1db3090fe587bd