[clang] [clang-format] Add ShortReturnTypeColumn option. (PR #78011)

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rmarker wrote:

Reworked this PR with a new approach, as discussed in #78010.

`ShortReturnTypeColumn` has been replaced with a new enum option `RTBS_AllowShortType` for `AlwaysBreakAfterReturnType `.
Also, the short return type behaviour has been updated to ignore the leading indentation on the line.

https://github.com/llvm/llvm-project/pull/78011