[clang] [llvm] Convert clang-format to Opt and add multicall support (PR #201730)

[David Zbarsky via cfe-commits]

dzbarsky wrote:

Hey all, apologies for putting up this PR without a summary. I've added one, hopefully it makes the motivation clearer. The implementation can likely be cleaned up but I didn't want to spend cycles on that without seeing if this patch has a chance of being upstreamed.

https://github.com/llvm/llvm-project/pull/201730