[clang] [CodeGen][NFC] Split __sized_by tests into their own file and rename test cases (PR #213793)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-aarch64-darwin` running on `doug-worker-4` while building `clang` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/190/builds/47232

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

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: Transforms/AtomicExpand/NVPTX/atomicrmw-vector.ll' FAILED ********************
Exit Code: 2

Command Output (stdout):
--
# RUN: at line 2
/Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/opt -S /Users/buildbot/buildbot-root/llvm-project/llvm/test/Transforms/AtomicExpand/NVPTX/atomicrmw-vector.ll -passes='require<libcall-lowering-info>,atomic-expand' -mtriple=nvptx64-nvidia-cuda -mcpu=sm_90 -mattr=+ptx83 | /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/FileCheck /Users/buildbot/buildbot-root/llvm-project/llvm/test/Transforms/AtomicExpand/NVPTX/atomicrmw-vector.ll
# executed command: /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/opt -S /Users/buildbot/buildbot-root/llvm-project/llvm/test/Transforms/AtomicExpand/NVPTX/atomicrmw-vector.ll '-passes=require<libcall-lowering-info>,atomic-expand' -mtriple=nvptx64-nvidia-cuda -mcpu=sm_90 -mattr=+ptx83
# .---command stderr------------
# | /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/opt: WARNING: failed to create target machine for 'nvptx64-nvidia-cuda': unable to get target for 'nvptx64-nvidia-cuda', see --version and --triple.
# | /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/opt: pass 'atomic-expand' requires TargetMachine
# `-----------------------------
# error: command failed with exit status: 1
# executed command: /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/FileCheck /Users/buildbot/buildbot-root/llvm-project/llvm/test/Transforms/AtomicExpand/NVPTX/atomicrmw-vector.ll
# .---command stderr------------
# | FileCheck error: '<stdin>' is empty.
# | FileCheck command line:  /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/FileCheck /Users/buildbot/buildbot-root/llvm-project/llvm/test/Transforms/AtomicExpand/NVPTX/atomicrmw-vector.ll
# `-----------------------------
# error: command failed with exit status: 2

--

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


```

</details>

https://github.com/llvm/llvm-project/pull/213793