Comment placement in argument lists causes ordering issues

This call:

list(
  # comment0
  foo  # comment1
  =1, bar  # comment2
  =  # comment3
  # comment4
  2 #comment5
  #comment6
  , #comment7
  #comment8
)

Is currently formatted as:

list(
  # comment0
  # comment1
  foo = 1,
  # comment3
  # comment4
  # comment2
  bar = 2, #comment5 #comment7
  #comment8
  #comment6
)

We need to fix these issues:

• comment2 is pulled down because it becomes a leading comment of the whole argument node
• comment6 is pulled down because it becomes a leading comment of the empty argument, I think because it's an own-line and the default placement puts it on the next node.
• comment7 is formatted on the same line as comment5, because they both become trailing comments of the same node, and both have lines_before = 0. This happens here: https://github.com/posit-dev/air/blob/e3655e9a68f18ba7caea0aa6680817553bc97bee/crates/air_r_formatter/src/comments.rs#L951

Start in crates/air_r_formatter/src/comments.rs at the referenced logic around line 951, using the issue's R call as the reproduction. Trace how comments around argument nodes and the empty argument are assigned, then verify that comment2, comment6, and comment7 retain the intended order and line placement without combining comments incorrectly.