[tools] Add clang_format_new.py to download, verify and run clang-format binary (#34566)
Summary:
**Summary**
This commit adds `tools/clang_format_new.py`, which downloads a platform-appropriate
clang-format binary to a `.gitignored` location, verifies the binary by comparing its
SHA1 hash to a reference hash (also included in this commit), and runs it on all files
matched a specific regex in a list of whitelisted subdirectories of pytorch.
This script will eventually replace `tools/clang_format.py`.
**Testing**
Ran the script.
*No Args*
```
pytorch > ./tools/clang_format.py
Downloading clang-format to /Users/<user>/Desktop/pytorch/.clang-format-bin
0% |################################################################| 100%
Using clang-format located at /Users/<user>/Desktop/pytorch/.clang-format-bin/clang-format
> echo $?
0
> git status
<bunch of files>
```
`--diff` *mode*
```
> ./tools/clang_format.py --diff
Using clang-format located at /Users/<user>/Desktop/pytorch/.clang-format-bin/clang-format
Some files are not formatted correctly
> echo $?
1
<format files using the script>
> ./tools/clang_format.py --diff
Using clang-format located at /Users/<user>/Desktop/pytorch/.clang-format-bin/clang-format
All files are formatted correctly
> echo $?
0
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34566
Differential Revision: D20431290
Pulled By: SplitInfinity
fbshipit-source-id: 3966f769cfb923e58ead9376d85e97127415bdc6
