clang-format: [JS] handle default bindings in imports.

clang-format: [JS] handle default bindings in imports.

Summary:
Default imports appear outside of named bindings in curly braces:

  import A from 'a';
  import A, {symbol} from 'a';

Reviewers: djasper

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D23973

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@280486 91177308-0d34-0410-b5e6-96231b3b80d8