clang-format: [JS] terminate import sorting on `export type X = Y`

Contributed by @jankuehle!

https://reviews.llvm.org/D150116 introduced a bug. `export type X = Y` was considered an export declaration and took part in import sorting. This is not correct. With this change `export type X = Y` properly terminates import sorting.

Reviewed By: krasimir

Differential Revision: https://reviews.llvm.org/D150563