clang-format: [JS] Initial support for regex literals.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208281 91177308-0d34-0410-b5e6-96231b3b80d8
clang-format: [JS] Support regex literals after 'return'.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208285 91177308-0d34-0410-b5e6-96231b3b80d8