[clang-format] Correctly attach enum braces with ShortEnums disabled

Previously, with AllowShortEnumsOnASingleLine disabled, enums that would have otherwise fit on a single line would always put the opening brace on its own line.
This patch ensures that these enums will only put the brace on its own line if the existing attachment rules indicate that it should.

Reviewed By: HazardyKnusperkeks, curdeius

Differential Revision: https://reviews.llvm.org/D99840