[clang] [clang-format] Support fine-grained alignment of variable declarations (PR #160270)

[James Henderson via cfe-commits]

jh7370 wrote:

This is heavily based on https://github.com/llvm/llvm-project/commit/f0bd62d8709a49dd87eb75411e41e2e11e0ab59d by @bradh352. Please let me know if I've missed anything, as this is my first clang-format contribution.

I'm not certain if what I've done to distinguish between a class and non-class variable declaration is the right approach, so any feedback would be greatly appreciated.

https://github.com/llvm/llvm-project/pull/160270