[clang-format] Break after string literals with trailing line breaks (#76795)

This restores a subset of functionality that was forego in
d68826df.

Streaming multiple string literals is rare enough in practice, hence
that change makes sense in general. But it seems people were
incidentally relying on this for having line breaks after string
literals that ended with `\n`.

This patch tries to restore that behavior to prevent regressions in the
upcoming LLVM release, until we can implement some configuration based
approach as proposed in https://github.com/llvm/llvm-project/pull/69859.