Trailing commas for multiline def / macro / fun parameter lists

[HertzDevil]

The formatter appends a comma to the last elements of multiline container literals:

[
  x,
  y, # this comma
]
{
  x,
  y,
}
{
  1 => x,
  2 => y,
}
{
  x: x,
  y: y,
}

to multiline type names (sometimes):

Tuple(Int32, String)

NamedTuple(
  x: Int32,
  y: String,
)

preserves it in multiline calls:

foo(
  1,
  2
)

foo(
  1,
  2,
)

but removes them from def parameter lists and similar nodes:

def foo(
  x,
  y
)
end

macro foo(
  x,
  y
)
end

fun foo(
  x : Int32,
  y : Int32
)
end

I think we should add the commas here too, unless the last parameter is a & or a .... This is to minimize diff noise when the parameters are moved around, added, or deleted. (By definition a block or a C vararg list must be the last parameter, so they aren't subject to this and can continue to have their trailing commas removed.)