Translate CpuAsk into admission control slot to use

Admission control slot accounting is described in IMPALA-8998. On each backend, number of. It compute 'slots_to_use' for each backend based on the max number of instances of any fragment on that backend. This is simplistic, because multiple fragments with same number of instance count, say 4 non-blocking fragments each with 12 instances, only request the max instance (12) admission slots rather than sum of it (48).

When COMPUTE_PROCESSING_COST is enabled, Planner will generate a CpuAsk number that represent the cpu requirement of that query over a particular executor group set. This number is an estimation of what is the largest number of query fragments that can run in-parallel given the blocking operator analysis. Therefore, the fragment trace that sums into that CpuAsk number can be translated into 'slots_to_use' as well, which will be a closer resemblance of maximum parallel execution of fragment instances.