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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> @AaronBallman can you help us clarify if this is an LLVM team decision that we need to follow, I'm more inclined to reject this (I see similar comments in clang-tidy PR)

There's no requirement to go this route, though having common option handling infrastructure between all the various tools is slightly beneficial in general (it makes it easier for someone working on one tool to know how to add a new option to another tool, but that doesn't come up all that often I think).

If this PR is going to move forward, please update the patch summary to describe why the changes are being made. See the developer policy on commit messages for further details: https://llvm.org/docs/DeveloperPolicy.html#commit-messages

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