Add a variant of auto formatting using clang-format that doesn't use
additional packages. It works by adding a buffer-local hook to
`'before-save` for all C++ project files.
Even though we tell the user to change the version manually if it
doesn't match with the current
`Toolchain/Local/i686/i686-pc-serenity/include/XX.X.X` version, it
doesn't hurt to update it properly now that versions differ by major
version.
