[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 `clang-x86_64-linux-abi-test` running on `sie-linux-worker2` while building `llvm` at step 6 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/8/builds/19599

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

```
Step 6 (build-unified-tree) failure: build (failure)
...
10.449 [6585/10/698] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CodeGen.cpp.o
10.467 [6584/10/699] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CodeGenCommonISel.cpp.o
10.493 [6583/10/700] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CommandFlags.cpp.o
10.526 [6582/10/701] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/ComplexDeinterleavingPass.cpp.o
10.542 [6581/10/702] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CriticalAntiDepBreaker.cpp.o
10.575 [6580/10/703] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/DeadMachineInstructionElim.cpp.o
10.580 [6579/10/704] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/DetectDeadLanes.cpp.o
10.621 [6578/10/705] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/DroppedVariableStatsMIR.cpp.o
10.638 [6577/10/706] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/DFAPacketizer.cpp.o
10.664 [6576/10/707] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/ProfDataUtils.cpp.o
FAILED: lib/IR/CMakeFiles/LLVMCore.dir/ProfDataUtils.cpp.o 
/opt/ccache/bin/g++ -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/buildbot/buildbot-root/abi-test/build/lib/IR -I/home/buildbot/buildbot-root/abi-test/llvm/llvm/lib/IR -I/home/buildbot/buildbot-root/abi-test/build/include -I/home/buildbot/buildbot-root/abi-test/llvm/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/buildbot/buildbot-root/abi-test/llvm/llvm/lib/IR/ProfDataUtils.cpp
/home/buildbot/buildbot-root/abi-test/llvm/llvm/lib/IR/ProfDataUtils.cpp: In function ‘llvm::SmallVector<unsigned int> llvm::downscaleWeights(llvm::ArrayRef<long unsigned int>, std::optional<long unsigned int>)’:
/home/buildbot/buildbot-root/abi-test/llvm/llvm/lib/IR/ProfDataUtils.cpp:282:10: error: could not convert ‘DownscaledWeights’ from ‘SmallVector<[...],4>’ to ‘SmallVector<[...],12>’
  282 |   return DownscaledWeights;
      |          ^~~~~~~~~~~~~~~~~
      |          |
      |          SmallVector<[...],4>
10.672 [6576/9/708] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/DwarfEHPrepare.cpp.o
10.676 [6576/8/709] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/EarlyIfConversion.cpp.o
12.674 [6576/7/710] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Function.cpp.o
12.791 [6576/6/711] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Instruction.cpp.o
15.447 [6576/5/712] Building AArch64GenInstrInfo.inc...
16.236 [6576/4/713] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Instructions.cpp.o
19.424 [6576/3/714] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Metadata.cpp.o
20.241 [6576/2/715] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Verifier.cpp.o
27.385 [6576/1/716] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CodeGenPrepare.cpp.o
ninja: build stopped: subcommand failed.

```

</details>

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