[llvm-branch-commits] [BOLT] Compute section utilization in heatmap (PR #139193)

[Amir Ayupov via llvm-branch-commits]

https://github.com/aaupov created https://github.com/llvm/llvm-project/pull/139193

Heatmap collects samples grouped by buckets. The size is configurable
via `--block-size`, with 64 bytes as the default (X86 cache line size).

Define section utilization as the number of buckets mapped to the
section with non-zero samples divided by the total number of buckets
covering the section.

Note that for buckets that cross section boundaries, we will attribute
the utilization to the first overlapping section.

Test Plan: updated heatmap-preagg.test