[bazel] create a clang-tidy binary target

Create a binary target for clang-tidy. Tested by running:

```
$ bazel build --config=generic_clang @llvm-project//clang-tools-extra/...
$ bazel test --config=generic_clang @llvm-project//clang-tools-extra/...
$ bazel run --config=generic_clang @llvm-project//clang-tools-extra/clang-tidy -- --help
```

Reviewed By: #bazel_build, aaronmondal

Differential Revision: https://reviews.llvm.org/D143804