[clang] [clang-format] Add option to remove leading blank lines (PR #91221)

[Owen Pan via cfe-commits]

owenca wrote:

I think this is a good time to combine the `KeepEmptyLines...` options. For example:
```
KeepEmptyLines:
  AtStartOfBlock: true
  AtStartOfFile: false
  AtEndOfFile: true
```

https://github.com/llvm/llvm-project/pull/91221