[display] signature completion with argument default values instead of just "?"

[Gama11]

This is basically another instance of #2561 as a reminder:

According to @nadako, this info should be easy to provide in his new Json-based display output.

[Simn]

This requires an appropriate structure to be defined in vshaxe first so I know what to target. Note that JsonFunctionSignature does not contain default values.

[Gama11]

Could we just add @:optional var value:String to JsonFunctionArgument to match what haxe.rtti.CType.FunctionArgument / dox has? Haxe doesn't have more info than that anyway, right?

[Simn]

It's a syntax expression, but we don't have a generate function for that yet.

[Gama11]

You mean for sending the default value as a proper expression structure rather than just a String? Hadn't really considered that, but that would probably be a good idea, especially if more complex default values such as enum values are allowed in the future..

[Gama11]

This is now fixed! \o/