clang-format: [JS] disable ASI on decorators.

Summary:
Automatic Semicolon Insertion in clang-format tries to guess if a line
wrap should insert an implicit semicolong. The previous heuristic would
not trigger ASI if a token was immediately preceded by an `@` sign:

    function foo(@Bar  // <-- does not trigger due to preceding @
                baz) {}

However decorators can have arbitrary parameters:

    function foo(@Bar(param, param, param)  // <-- precending @ missed
                baz) {}

While it would be possible to precisely find the matching `@`, just
conversatively disabling ASI for the entire line is simpler, while also
not regressing ASI substatially.

Reviewers: djasper

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D40410

llvm-svn: 318973