[llvm] [BOLT][heatmap] Produce zoomed-out heatmaps (PR #140153)

[Maksim Panchenko via llvm-commits]

https://github.com/maksfb commented:

The implementation looks good to me.

A couple comments regarding the interface:
  * If we are producing multiple files by default, we might have to change docs in more places.
  * I find the power-of-two limitation for the scale unnecessary.
  * The variance in default scale steps looks a bit unnatural (64, 4, 64 again). I would keep just 64 and 64 making the default sizes 64 bytes, 4 KB, 256 KB.

https://github.com/llvm/llvm-project/pull/140153