[llvm] Reland "[NFC] Move DroppedVariableStats to its own file and redesign it to be extensible (#118546)" (PR #119048)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-nvptx-nvidia-ubuntu` running on `as-builder-7` while building `llvm-project,llvm` at step 6 "test-build-unified-tree-check-llvm".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/180/builds/9652

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

```
Step 6 (test-build-unified-tree-check-llvm) failure: test (failure)
...
1.140 [4/7/680] Linking CXX executable unittests/tools/llvm-exegesis/LLVMExegesisTests
1.187 [4/6/681] Linking CXX executable unittests/Frontend/LLVMFrontendTests
1.442 [4/5/682] Linking CXX executable unittests/Support/SupportTests
1.453 [4/4/683] Linking CXX executable unittests/ADT/ADTTests
9.246 [4/3/684] Building CXX object unittests/CodeGen/CMakeFiles/CodeGenTests.dir/DroppedVariableStatsIRTest.cpp.o
9.539 [3/3/685] Linking CXX executable unittests/CodeGen/CodeGenTests
12.059 [3/2/686] Building CXX object unittests/Analysis/CMakeFiles/AnalysisTests.dir/FunctionPropertiesAnalysisTest.cpp.o
12.424 [2/2/687] Linking CXX executable unittests/Analysis/AnalysisTests
13.397 [2/1/688] Building CXX object unittests/IR/CMakeFiles/IRTests.dir/PassManagerTest.cpp.o
13.855 [1/1/689] Linking CXX executable unittests/IR/IRTests
FAILED: unittests/IR/IRTests 
: && /usr/bin/c++ -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -fno-lifetime-dse -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 -fuse-ld=gold     -Wl,--gc-sections unittests/IR/CMakeFiles/IRTests.dir/AbstractCallSiteTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/AsmWriterTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/AttributesTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/BasicBlockTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/BasicBlockDbgInfoTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/CFGBuilder.cpp.o unittests/IR/CMakeFiles/IRTests.dir/ConstantFPRangeTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/ConstantRangeTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/ConstantRangeListTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/ConstantsTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/DataLayoutTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/DebugInfoTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/DebugTypeODRUniquingTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/DemandedBitsTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/DominatorTreeTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/DominatorTreeBatchUpdatesTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/FunctionTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/PassBuilderCallbacksTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/IRBuilderTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/InstructionsTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/IntrinsicsTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/LegacyPassManagerTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/MDBuilderTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/MemoryModelRelaxationAnnotationsTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/ManglerTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/MetadataTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/ModuleTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/ModuleSummaryIndexTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/PassManagerTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/PatternMatch.cpp.o unittests/IR/CMakeFiles/IRTests.dir/ShuffleVectorInstTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/StructuralHashTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/TimePassesTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/TypesTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/UseTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/UserTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/ValueHandleTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/ValueMapTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/ValueTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/VectorBuilderTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/VectorTypesTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/VerifierTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/VFABIDemanglerTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/VPIntrinsicTest.cpp.o unittests/IR/CMakeFiles/IRTests.dir/CoreBindings.cpp.o -o unittests/IR/IRTests  -Wl,-rpath,/home/buildbot/worker/as-builder-7/ramdisk/llvm-nvptx-nvidia-ubuntu/build/lib  lib/libLLVMPasses.so.20.0git  lib/libllvm_gtest_main.so.20.0git  lib/libLLVMTestingSupport.so.20.0git  lib/libLLVMScalarOpts.so.20.0git  lib/libLLVMTransformUtils.so.20.0git  lib/libLLVMAnalysis.so.20.0git  lib/libLLVMAsmParser.so.20.0git  lib/libLLVMCore.so.20.0git  lib/libLLVMTargetParser.so.20.0git  lib/libllvm_gtest.so.20.0git  lib/libLLVMSupport.so.20.0git  -Wl,-rpath-link,/home/buildbot/worker/as-builder-7/ramdisk/llvm-nvptx-nvidia-ubuntu/build/lib && :
unittests/IR/CMakeFiles/IRTests.dir/PassManagerTest.cpp.o:PassManagerTest.cpp:function llvm::StandardInstrumentations::~StandardInstrumentations(): error: undefined reference to 'vtable for llvm::DroppedVariableStatsIR'
/usr/bin/ld.gold: the vtable symbol may be undefined because the class is missing its key function
unittests/IR/CMakeFiles/IRTests.dir/PassManagerTest.cpp.o:PassManagerTest.cpp:function llvm::StandardInstrumentations::~StandardInstrumentations(): error: undefined reference to 'llvm::DroppedVariableStats::~DroppedVariableStats()'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/119048