JavaScript allows parameter lists to include trailing commas:

    myFunction(param1, param2,);

For symmetry with other parenthesized lists ([...], {...}), clang-format should
wrap parenthesized lists one-per-line if they contain a trailing comma:

    myFunction(
        param1,
        param2,
    );

This is particularly useful in function declarations or calls with many
arguments, e.g. commonly in constructors.

Differential Revision: https://reviews.llvm.org/D33023

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@303049 91177308-0d34-0410-b5e6-96231b3b80d8