Add .git-blame-ignore-revs (#2036)
Add .git-blame-ignore-revs (#2036)

This adds .git-blame-ignore-revs file, which was supported since version
2.23 (Aug 2019), which lets `git blame` ignore specified revisions.
Usage examples:
https://github.com/llvm/llvm-project/blob/main/.git-blame-ignore-revs
https://github.com/WebAssembly/binaryen/blob/main/.git-blame-ignore-revs

This currently contains a clang-format commit (#1684).
WebAssembly/wabt,WebAssembly/wabt,WebAssembly/wabt,WebAssembly/wabt,WebAssembly/wabt