[clang-format] extern with new line brace without indentation

https://github.com/llvm/llvm-project/issues/49804

Interaction between IndentExternBlock and AfterExternBlock means you cannot have AfterExternBlock = true and IndentExternBlock = NoIndent/Indent

This patch resolves that
```
BraceWrapping:
  AfterExternBlock: true
IndentExternBlock: AfterExternBlock
```
Fixes: #49804

Reviewed By: HazardyKnusperkeks, curdeius, owenpan

Differential Revision: https://reviews.llvm.org/D115879