[clang] [clang-format] Correctly compute SplitPenalty of TrailingReturnArrow (PR #105613)

[Owen Pan via cfe-commits]

owenca wrote:

After reviewing commit e00d32afb9d33a1eca48e2b041c9688436706c5b, I've come to the conclusion that it would be better to revert it and keep lambda arrows differentiated from function arrows.

https://github.com/llvm/llvm-project/pull/105613