[llvm] [CAS] Add UnifiedOnDiskCache and OnDiskCAS (PR #114103)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-expensive-checks-win` running on `as-worker-93` while building `llvm` at step 7 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/14/builds/4601

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

```
Step 7 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM-Unit :: CAS/./CASTests.exe/31/36' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:C:\a\llvm-clang-x86_64-expensive-checks-win\build\unittests\CAS\.\CASTests.exe-LLVM-Unit-14840-31-36.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=36 GTEST_SHARD_INDEX=31 C:\a\llvm-clang-x86_64-expensive-checks-win\build\unittests\CAS\.\CASTests.exe
--

Script:
--
C:\a\llvm-clang-x86_64-expensive-checks-win\build\unittests\CAS\.\CASTests.exe --gtest_filter=OnDiskCAS/CASTest.BlobsBigParallel/0
--
C:\a\llvm-clang-x86_64-expensive-checks-win\llvm-project\llvm\unittests\CAS\ObjectStoreTest.cpp(315): error: Value of: llvm::detail::TakeError(CAS->getProxy(*ID).moveInto(Node))
Expected: succeeded
  Actual: failed  ('C:\Users\Buildbot\AppData\Local\Temp\lit-tmp-myr7yuce\on-disk-cas-1cec22\leaf+0.13304.v1': no such file or directory)

C:\a\llvm-clang-x86_64-expensive-checks-win\llvm-project\llvm\unittests\CAS\ObjectStoreTest.cpp(315): error: Value of: llvm::detail::TakeError(CAS->getProxy(*ID).moveInto(Node))
Expected: succeeded
  Actual: failed  ('C:\Users\Buildbot\AppData\Local\Temp\lit-tmp-myr7yuce\on-disk-cas-1cec22\leaf+0.13184.v1': no such file or directory)


C:\a\llvm-clang-x86_64-expensive-checks-win\llvm-project\llvm\unittests\CAS\ObjectStoreTest.cpp:315
Value of: llvm::detail::TakeError(CAS->getProxy(*ID).moveInto(Node))
Expected: succeeded
  Actual: failed  ('C:\Users\Buildbot\AppData\Local\Temp\lit-tmp-myr7yuce\on-disk-cas-1cec22\leaf+0.13304.v1': no such file or directory)

C:\a\llvm-clang-x86_64-expensive-checks-win\llvm-project\llvm\unittests\CAS\ObjectStoreTest.cpp:315
Value of: llvm::detail::TakeError(CAS->getProxy(*ID).moveInto(Node))
Expected: succeeded
  Actual: failed  ('C:\Users\Buildbot\AppData\Local\Temp\lit-tmp-myr7yuce\on-disk-cas-1cec22\leaf+0.13184.v1': no such file or directory)



********************


```

</details>

https://github.com/llvm/llvm-project/pull/114103