[clang] [clang-format] Adjust requires clause wrapping (#101550) (PR #102078)

[Nathan Sidwell via cfe-commits]

urnathan wrote:

> But that would be the way to go, add an option to the enum, don't change the existing behavior.

Sure -- I thought I'd shoot for the simplest change first :)

Here's an update that adds `OwnLineWithBrace`, which is like `OwnLine` except it also allows a trailing `{` (and anything that would then enable).  I describe the formatting in terms of the syntax (`{`) rather than semantics (function definition), to future proof it, should perhaps requires clauses be permitted at other brace-preceding locations. 

https://github.com/llvm/llvm-project/pull/102078