Inserts text at position in the list of strings stored in this.
If id is non-null then it is used as the ID of the row. See [
[email protected]:id-column].
If position is negative then text is appended.
| this |
A `GtkComboBoxText` |
| position |
An index to insert |
| id |
a string ID for this value |
| text |
A string to display |