[clang-format] Style to separate definition blocks

This commit resolves GitHub issue #45895 (Bugzilla #46550), to
add or remove empty line between definition blocks including
namespaces, classes, structs, enums and functions.

Reviewed By: MyDeveloperDay, curdeius, HazardyKnusperkeks

Differential Revision: https://reviews.llvm.org/D116314