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

[Maksim Panchenko via llvm-commits]

maksfb wrote:

Instead of introducing the new option, can we reuse `--block-size=` and make it accept multiple values or a different format?

> If rescaling is impossible, no heatmap is produced.

Without a printed warning? I understand that the size limitation is driven by implementation, but at the very least we should report that there is no expected output.

Alternatively, use a different option format that encapsulates the limitations. E.g., `--block-size=<initial_size>{:<scale>:<count>}` or `--block-size=<initial_size>{:<scale1>,<scale2>...}`.

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