New parameter added by a splice gets the position of an existing one #1838

mxcli: v0.31.0
Mendix: 11.12.4

What happens

When create or modify adds a parameter between existing ones, the new parameter gets the next free slot to the right of the parameter before it. The existing parameters keep their stored positions and are not moved, so the new parameter lands exactly on top of the next one.

In Studio Pro the two parameter icons overlap, and $Extra is hidden behind $List. Behaviour is unchanged.

Afterwards DESCRIBE prints @position(300, 53) before $List only, so the overlap also survives a later drop + create (#1831).

Reproduction

1. Create the flow from drop + create in one script loses documentation and Mark as used #1831 (parameters $Count: Integer and $List: List of System.User, no @position on parameters). Stored positions: $Count 200;53, $List 300;53.
2. Run create or modify with the same body and one parameter added in the middle:

create or modify microflow ReproModule.ACT_docs_layout (
  $Count: Integer,
  $Extra: String,
  $List: List of System.User
)

3. bson dump: $Extra and $List both have RelativeMiddlePoint 300;53.

Expected

The new parameter gets a position no other parameter uses, for example after the last parameter. Or the parameters after it shift one slot to the right.