Didn't `SyntaxEditor::add_annotation` consider change offset?

I am working on an assist, but it seems that the SyntaxEditor::add_annotation #15710 has not taken into account any editing offset, which makes it difficult to use.

Is this normal?

|builder: &mut SourceChangeBuilder| {
    let mut edit = builder.make_editor(fn_.syntax());

    // Insert 2 byte whitespace
    edit.insert(Position::before(fn_.syntax()), make::tokens::whitespace("  "));

    if let Some(cap) = ctx.config.snippet_cap {
        let annotation = builder.make_tabstop_after(cap);
        edit.add_annotation(fn_.syntax(), annotation);
    }

    builder.add_file_edits(ctx.vfs_file_id(), edit);
},

Input:

impl Foo {
    fn foo(&self) -> &i32 {
        &self.0
    }
}

Current output:

impl Foo {
      fn foo(&self) -> &i32 {
        &self.0
   $0 }
}

Expect output:

impl Foo {
      fn foo(&self) -> &i32 {
        &self.0
    }$0
}

Start at SyntaxEditor::add_annotation and reproduce the SourceChangeBuilder example from the issue, including the two-byte whitespace insertion. Trace how the editing offset is handled for the annotation, then verify that the tabstop appears after the closing brace as shown in the expected output.