clang-format: [JS] Support alternative operator names as identifiers.

Before:
  not. and . or . not_eq = 1;

After:
  not.and.or.not_eq = 1;

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217179 91177308-0d34-0410-b5e6-96231b3b80d8