clang-format: [JS] Handle certain cases of ASI.

Automatic Semicolon Insertion can only be properly handled by parsing
source code. However conservatively catching just a few, common
situations prevents breaking code during development, which greatly
improves usability.

JS code should still use semicolons, and ASI code should be flagged by
a compiler or linter.

Patch by Martin Probst. Thank you.

llvm-svn: 263470