[clang-tools-extra] [clang-tidy] Improve `readability-function-size`: count class member initializers as statements (PR #131669)

[Baranov Victor via cfe-commits]

vbvictor wrote:

Opening this PR because previous PR changing `readability-function-size` check was not merger for more than a month.

https://github.com/llvm/llvm-project/pull/131669