clang-format: [JS] handle object literals with casts.

Summary: E.g. `{a: 1} as b`.

Reviewers: djasper

Subscribers: cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D23714

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@279250 91177308-0d34-0410-b5e6-96231b3b80d8