[clang-format] PR16518 Add flag to suppress empty line insertion before access modifier

Add new option called InsertEmptyLineBeforeAccessModifier. Empty line
before access modifier is inerted if this option is set to true (which
is the default value, because clang-format always inserts empty lines
before access modifiers), otherwise empty lines are removed.

Fixes issue #16518.

Differential Revision: https://reviews.llvm.org/D93846