[llvm] [NFC][PGO] Factor downscaling of branch weights out of `Instrumentation` into `ProfileData` (PR #153735)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `polly-x86_64-linux-plugin` running on `polly-x86_64-gce1` while building `llvm` at step 5 "build".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/158/builds/10638

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 5 (build) failure: 'ninja' (failure)
[1/191] Generating VCSRevision.h
[2/191] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/ProfDataUtils.cpp.o
FAILED: lib/IR/CMakeFiles/LLVMCore.dir/ProfDataUtils.cpp.o 
ccache /usr/bin/c++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.obj/lib/IR -I/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/lib/IR -I/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.obj/include -I/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -std=c++17 -MD -MT lib/IR/CMakeFiles/LLVMCore.dir/ProfDataUtils.cpp.o -MF lib/IR/CMakeFiles/LLVMCore.dir/ProfDataUtils.cpp.o.d -o lib/IR/CMakeFiles/LLVMCore.dir/ProfDataUtils.cpp.o -c /home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/lib/IR/ProfDataUtils.cpp
/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/lib/IR/ProfDataUtils.cpp: In function ‘llvm::SmallVector<unsigned int> llvm::downscaleWeights(llvm::ArrayRef<long unsigned int>, std::optional<long unsigned int>)’:
/home/worker/buildbot-workers/polly-x86_64-gce1/rundir/llvm.src/llvm/lib/IR/ProfDataUtils.cpp:282:10: error: could not convert ‘DownscaledWeights’ from ‘SmallVector<[...],4>’ to ‘SmallVector<[...],12>’
  282 |   return DownscaledWeights;
      |          ^~~~~~~~~~~~~~~~~
      |          |
      |          SmallVector<[...],4>
[3/191] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/MDBuilder.cpp.o
[4/191] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Function.cpp.o
[5/191] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Instruction.cpp.o
[6/191] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Instructions.cpp.o
[7/191] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Metadata.cpp.o
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/153735