A  Clang-Format configuration to make the closure definition block to
be properly recognized as such.

Also small wrapper macro to avoid comma in the actual definition code
which was causing unwanted indentation of parameters definition.

Requires Clang-Format 7 or newer. The version we ship in the libs is
12, so for recommended development setup it should all be good.

Differential Revision: https://developer.blender.org/D12920