[llvm] [NFC][DirectX] Refactor `DXILPrepare`/`DXILTranslateMetadata` (PR #164285)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-aarch64-quick` running on `linaro-clang-aarch64-quick` while building `llvm` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/65/builds/24501

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

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clangd Unit Tests :: ./ClangdTests/62/335' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests-Clangd Unit Tests-1689720-62-335.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=335 GTEST_SHARD_INDEX=62 /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests
--

Script:
--
/home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests --gtest_filter=ClangdThreadingTest.StressTest
--
File version went from null to null
File version went from null to null
File version went from null to null
File version went from null to null
File version went from null to null
ASTWorker skipping Update for /clangd-test/Foo1.cpp
ASTWorker skipping Update for /clangd-test/Foo1.cpp
File version went from null to null
File version went from null to null
File version went from null to null
File version went from null to null
ASTWorker skipping Update for /clangd-test/Foo4.cpp
File version went from null to null
File version went from null to null
File version went from null to null
File version went from null to null
File version went from null to null
ASTWorker skipping Update for /clangd-test/Foo0.cpp
File version went from null to null
ASTWorker building file /clangd-test/Foo2.cpp version null with command 
[/clangd-test]
clang -ffreestanding /clangd-test/Foo2.cpp
ASTWorker skipping Update for /clangd-test/Foo4.cpp
ASTWorker building file /clangd-test/Foo3.cpp version null with command 
[/clangd-test]
clang -ffreestanding /clangd-test/Foo3.cpp
ASTWorker building file /clangd-test/Foo4.cpp version null with command 
[/clangd-test]
clang -ffreestanding /clangd-test/Foo4.cpp
ASTWorker building file /clangd-test/Foo1.cpp version null with command 
[/clangd-test]
clang -ffreestanding /clangd-test/Foo1.cpp
Driver produced command: cc1 -cc1 -triple aarch64-unknown-linux-gnu -fsyntax-only -disable-free -clear-ast-before-backend -main-file-name Foo1.cpp -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=non-leaf -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -ffreestanding -enable-tlsdesc -target-cpu generic -target-feature +v8a -target-feature +fp-armv8 -target-feature +neon -target-abi aapcs -debugger-tuning=gdb -fdebug-compilation-dir=/clangd-test -fcoverage-compilation-dir=/clangd-test -resource-dir lib/clang/22 -internal-isystem lib/clang/22/include -internal-isystem /usr/local/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -ferror-limit 19 -fno-signed-char -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fcxx-exceptions -fexceptions -no-round-trip-args -target-feature -fmv -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -x c++ /clangd-test/Foo1.cpp
Driver produced command: cc1 -cc1 -triple aarch64-unknown-linux-gnu -fsyntax-only -disable-free -clear-ast-before-backend -main-file-name Foo4.cpp -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=non-leaf -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -ffreestanding -enable-tlsdesc -target-cpu generic -target-feature +v8a -target-feature +fp-armv8 -target-feature +neon -target-abi aapcs -debugger-tuning=gdb -fdebug-compilation-dir=/clangd-test -fcoverage-compilation-dir=/clangd-test -resource-dir lib/clang/22 -internal-isystem lib/clang/22/include -internal-isystem /usr/local/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -ferror-limit 19 -fno-signed-char -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fcxx-exceptions -fexceptions -no-round-trip-args -target-feature -fmv -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -x c++ /clangd-test/Foo4.cpp
ASTWorker building file /clangd-test/Foo4.cpp version null with command 
[/clangd-test]
clang -ffreestanding /clangd-test/Foo4.cpp
Driver produced command: cc1 -cc1 -triple aarch64-unknown-linux-gnu -fsyntax-only -disable-free -clear-ast-before-backend -main-file-name Foo4.cpp -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=non-leaf -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -ffreestanding -enable-tlsdesc -target-cpu generic -target-feature +v8a -target-feature +fp-armv8 -target-feature +neon -target-abi aapcs -debugger-tuning=gdb -fdebug-compilation-dir=/clangd-test -fcoverage-compilation-dir=/clangd-test -resource-dir lib/clang/22 -internal-isystem lib/clang/22/include -internal-isystem /usr/local/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -ferror-limit 19 -fno-signed-char -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fcxx-exceptions -fexceptions -no-round-trip-args -target-feature -fmv -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -x c++ /clangd-test/Foo4.cpp
ASTWorker building file /clangd-test/Foo0.cpp version null with command 
[/clangd-test]
...

```

</details>

https://github.com/llvm/llvm-project/pull/164285