[llvm-profgen] Allow unsymbolized profile as perf input

This change allows the unsymbolized profile as input. The unsymbolized profile is created by `llvm-profgen` with `--skip-symbolization` and it's after the sample aggregation but before symbolization , so it has much small file size. It can be used for sample merging and trimming,  also is useful for debugging or adding test cases. A switch `--unsymbolized-profile=file-patch` is added for this.

Format of unsymbolized profile:
```

   [context stack1]    # If it's a CS profile
      number of entries in RangeCounter
      from_1-to_1:count_1
      from_2-to_2:count_2
      ......
      from_n-to_n:count_n
      number of entries in BranchCounter
      src_1->dst_1:count_1
      src_2->dst_2:count_2
      ......
      src_n->dst_n:count_n
    [context stack2]
      ......
```

Reviewed By: hoy, wenlei

Differential Revision: https://reviews.llvm.org/D111750