Revert "[SampleFDO] Reapply: Refactor SampleProfile.cpp"

Revert "[SampleFDO] Add missing #includes to unbreak modules build after D96455"

This reverts commit c73cbf2.

Revert "[SampleFDO] Fix MSVC "namespace uses itself" warning (NFC)"

This reverts commit a23e6b3.

Revert "[SampleFDO] Reapply: Refactor SampleProfile.cpp"

This reverts commit 6fd5ccf.

Still seeing link failures when building llc (or other tools), due to
the new SampleProfileLoaderBaseImpl.h containing definitions that get
duplicated across multiple TU's.

```
duplicate symbol 'llvm::SampleProfileLoaderBaseImpl::findEquivalenceClasses(llvm::Function&)' in:
    tools/llc/CMakeFiles/llc.dir/llc.cpp.o
    lib/libLLVMInstCombine.a(InstCombineVectorOps.cpp.o)
duplicate symbol 'llvm::SampleProfileLoaderBaseImpl::buildEdges(llvm::Function&)' in:
    tools/llc/CMakeFiles/llc.dir/llc.cpp.o
    lib/libLLVMInstCombine.a(InstCombineVectorOps.cpp.o)
duplicate symbol 'llvm::SampleProfileLoaderBaseImpl::computeDominanceAndLoopInfo(llvm::Function&)' in:
    tools/llc/CMakeFiles/llc.dir/llc.cpp.o
    lib/libLLVMInstCombine.a(InstCombineVectorOps.cpp.o)
duplicate symbol 'llvm::SampleProfileLoaderBaseImpl::getFunctionLoc(llvm::Function&)' in:
    tools/llc/CMakeFiles/llc.dir/llc.cpp.o
    lib/libLLVMInstCombine.a(InstCombineVectorOps.cpp.o)
duplicate symbol 'llvm::SampleProfileLoaderBaseImpl::getBlockWeight(llvm::BasicBlock const*)' in:
    tools/llc/CMakeFiles/llc.dir/llc.cpp.o
    lib/libLLVMInstCombine.a(InstCombineVectorOps.cpp.o)
duplicate symbol 'llvm::SampleProfileLoaderBaseImpl::printBlockWeight(llvm::raw_ostream&, llvm::BasicBlock const*) const' in:
    tools/llc/CMakeFiles/llc.dir/llc.cpp.o
    lib/libLLVMInstCombine.a(InstCombineVectorOps.cpp.o)
duplicate symbol 'llvm::SampleProfileLoaderBaseImpl::printBlockEquivalence(llvm::raw_ostream&, llvm::BasicBlock const*)' in:
    tools/llc/CMakeFiles/llc.dir/llc.cpp.o
    lib/libLLVMInstCombine.a(InstCombineVectorOps.cpp.o)
duplicate symbol 'llvm::SampleProfileLoaderBaseImpl::printEdgeWeight(llvm::raw_ostream&, std::__1::pair<llvm::BasicBlock const*, llvm::BasicBlock const*>)' in:
    tools/llc/CMakeFiles/llc.dir/llc.cpp.o
    lib/libLLVMInstCombine.a(InstCombineVectorOps.cpp.o)
```

Author: vedantk