Make accessible-position-in-set zero-based

Author: DataTriny

docs/reference/src/language/builtins/elements.md

@@ -78,7 +78,7 @@ Use the following `accessible-` properties to make your items interact well with
 -   **`accessible-placeholder-text`** (_in_ _string_): A placeholder text to use when the item's value is empty. Applies to text elements.
 -   **`accessible-selectable`** (_in_ _bool_): Whether the element can be selected or not.
 -   **`accessible-selected`** (_in_ _bool_): Whether the element is selected or not. This maps to the "is-selected" state of listview items.
--   **`accessible-position-in-set`** (_in_ _int_): The index (starting from 1) of this element in a group of similar elements. Applies to list items, radio buttons and other elements.
+-   **`accessible-position-in-set`** (_in_ _int_): The index (starting from 0) of this element in a group of similar elements. Applies to list items, radio buttons and other elements.
 -   **`accessible-size-of-set`** (_in_ _int_): The total number of elements in a group. Applies to all elements of a group like list items, radio buttons and other elements, but not to their parent container like list views, radio button groups or other grouping elements.
 
 You can also use the following callbacks that are going to be called by the accessibility framework:

internal/compiler/widgets/cosmic/components.slint

@@ -107,7 +107,7 @@ export component ListItem {
     accessible-label: root.item.text;
     accessible-selectable: true;
     accessible-selected: root.is-selected;
-    accessible-position-in-set: root.index + 1;
+    accessible-position-in-set: root.index;
     accessible-size-of-set: root.total-items;
 
     states [

internal/compiler/widgets/cupertino/components.slint

@@ -63,7 +63,7 @@ export component ListItem {
     accessible-label: root.item.text;
     accessible-selectable: true;
     accessible-selected: root.is-selected;
-    accessible-position-in-set: root.index + 1;
+    accessible-position-in-set: root.index;
     accessible-size-of-set: root.total-items;
 
     states [

internal/compiler/widgets/fluent/components.slint

@@ -51,7 +51,7 @@ export component ListItem {
     accessible-label: root.item.text;
     accessible-selectable: true;
     accessible-selected: root.is-selected;
-    accessible-position-in-set: root.index + 1;
+    accessible-position-in-set: root.index;
     accessible-size-of-set: root.total-items;
 
     states [

internal/compiler/widgets/material/components.slint

@@ -109,7 +109,7 @@ export component ListItem {
     accessible-label: root.item.text;
     accessible-selectable: true;
     accessible-selected: root.is-selected;
-    accessible-position-in-set: root.index + 1;
+    accessible-position-in-set: root.index;
     accessible-size-of-set: root.total-items;
 
     states [