[clang] [clang-format] Add options to control wrapped lambda brace indent. (PR #143249)

[via cfe-commits]

rmarker wrote:

> Something here doesn't feel right..aren't these brace Wapping options?

Yes, the `BraceWrapping` options contain `IndentBraces`.
This is so that `BreakBeforeBraces: Custom` can also indent braces, similar to `BreakBeforeBraces: GNU`.
`GNU` was recently updated (https://github.com/llvm/llvm-project/pull/135479) to also indent lambda braces.
The aim of this PR is to allow for more control of how lambda braces are indented when using the `Custom` mode.

Holistically, it might make more sense to split indentation, and thus `GNU` and `Whitesmiths`, out of brace wrapping. But I'm not sure whether a change like that would be worthwhile at this point.

https://github.com/llvm/llvm-project/pull/143249