See editorconfig.org for details of the format. This is a first attempt at describing our coding style in editorconfig syntax.
Inspired by !308 (merged). editorconfig is less powerful than clang-format, but also more universal: basically all programmer-oriented text editors have a concept of toggling settings for indent size and whether to indent with hard tabs or spaces, even if they cannot understand the finer points of GNU-style brace positioning.
This should make it a lot less necessary to add vim modelines and Emacs local variables to source files as we have historically done: vim and emacs both have editorconfig plugins available.