feat(multi-select): add itemToProp to customize name, title, labelText values passed to input (#1074)

Currently, the input `name` for each item uses the same value as `itemToString(item)`.

This adds an `itemToInput` prop to allow the consumer to customize the name/title/labelText values passed to the `Checkbox` input.

The name attribute now defaults to use the `item.id` instead of `item.text`.

docs/src/COMPONENT_API.json

@@ -6446,6 +6446,17 @@
           "constant": false,
           "reactive": false
         },
+        {
+          "name": "itemToInput",
+          "kind": "let",
+          "description": "Override the item name, title, labelText passed to the checkbox input",
+          "type": "(item: MultiSelectItem) => { name?: string; labelText?: any; title?: string; }",
+          "value": "(item) => {}",
+          "isFunction": true,
+          "isFunctionDeclaration": false,
+          "constant": false,
+          "reactive": false
+        },
         {
           "name": "selectedIds",
           "kind": "let",