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

Add a capability to produce multiple heatmaps with given bucket sizes.

The default heatmap block size (64B) could be too fine-grained for
large binaries. Extend the option `block-size` to accept a list of
bucket sizes for additional heatmaps with coarser granularity. The
heatmap is simply rescaled so provided sizes should be multiples of
each other. Human-readable suffixes can be used, e.g. 4K, 16kb, 1MiB.

New defaults: 64B (base bucket size), 4KB (default page size),
256KB (for large binaries).

Test Plan: updated heatmap-preagg.test

bolt/tools/heatmap/heatmap.cpp

@@ -59,7 +59,26 @@ static std::string GetExecutablePath(const char *Argv0) {
 
 int main(int argc, char **argv) {
   cl::HideUnrelatedOptions(ArrayRef(opts::HeatmapCategories));
-  cl::ParseCommandLineOptions(argc, argv, "");
+  cl::ParseCommandLineOptions(
+      argc, argv,
+      " BOLT Code Heatmap tool\n\n"
+      "  Produces code heatmaps using sampled profile\n\n"
+
+      "  Inputs:\n"
+      "  - Binary (supports BOLT-optimized binaries),\n"
+      "  - Sampled profile collected from the binary:\n"
+      "    - perf data or pre-aggregated profile data (instrumentation profile "
+      "not supported)\n"
+      "    - perf data can have basic (IP) or branch-stack (LBR) samples\n\n"
+
+      "  Outputs:\n"
+      "  - Heatmaps: colored ASCII (requires a color-capable terminal or a"
+      " conversion tool like `aha`)\n"
+      "    Multiple heatmaps are produced by default with different "
+      "granularities (set by `block-size` option)\n"
+      "  - Section hotness: per-section samples% and utilization%\n"
+      "  - Cumulative distribution: working set size corresponding to a "
+      "given percentile of samples\n");
 
   if (opts::PerfData.empty()) {
     errs() << ToolName << ": expected -perfdata=<filename> option.\n";