Add more than one variable arguments.

[ykmnkmi]

For example Element methods with variable arguments, instead of a single argument:

external void prepend(JSAny nodes);
external void append(JSAny nodes);
external void before(JSAny nodes);
external void after(JSAny nodes);

generate rest arguments as optional positional arguments:

external void prepend(JSAny node, [JSAny node2, JSAny node3, ..., JSAny node9]);
external void append(JSAny node, [JSAny node2, JSAny node3, ..., JSAny node9]);
external void before(JSAny node, [JSAny node2, JSAny node3, ..., JSAny node9]);
external void after(JSAny node, [JSAny node2, JSAny node3, ..., JSAny node9]);

I have some cases with 2 ~ 4 arguments. Currently, I use extension types and dart:js_interop (target.callMethod('append'.toJS, node1, node2);)

Also, nodes for a single argument name sounds like it expect list of nodes, instead one node.

[srujzs]

Indeed, it's misleading and we should really be providing multiple arguments. We've been typically implementing variadic arguments as ~4 arguments in the SDK (callMethod from dart:js_interop_unsafe for example) so I'm tempted to keep it aligned there.

[ykmnkmi]

@srujzs I can work on this issue.

[srujzs]

Thanks, go for it! Happy to review the PR and answer any questions about the translator.

#339 is also related if you think it would make sense to do at the same time.