Optimize pending job queue iteration.

Batch the jobs pulled during iteration so that we pull several of an
app's jobs from the queue sequentially (resulting in some out of order
pulls) instead of pulling purely based on the sort order. Batching it
this way will mean we try to run several jobs of the same app at the
same, resulting in fewer process restarts, and can allow the iteration
runtime to amortize to O(A*J) instead of O(A*J*log(A)) for A <= 33,
where A = # apps and J = average # jobs per app.

Bug: 204924801
Test: atest FrameworksServicesTests:PendingJobQueueTest
Change-Id: I4d3dc17afb4d4ab0fb573d75a319bdb20a68c634