[llvm-profgen][CSSPGO] Support count based aggregated type of hybrid perf script

This change tried to integrate a new count based aggregated type of perf script. The only difference of the format is that an aggregated count is added at the head of the original sample which means the same samples are repeated to the given count times. This is used to reduce the perf script size.
e.g.
```
2
	          4005dc
	          400634
	          400684
	    7f68c5788793
 0x4005c8/0x4005dc/P/-/-/0  ....
```
Implemented by a dedicated PerfReader `AggregatedHybridPerfReader`.

Differential Revision: https://reviews.llvm.org/D107192