chore(item): add deprecated flag to fill prop (#28210)

Issue number: N/A

---------

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## What is the current behavior?
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The `fill` prop on `ion-item` is currently deprecated (see warning
[here](https://github.com/ionic-team/ionic-framework/blob/main/core/src/components/item/item.tsx#L248-L253))
but the docs have not been updated to reflect this.

## What is the new behavior?
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this PR. -->

`@deprecated` flag added to the `fill` prop.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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and migration path for existing applications below. -->


## Other information

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screenshots of how the component looks before and after the change. -->

Author: averyjohnston

core/src/components.d.ts

@@ -1336,6 +1336,7 @@ export namespace Components {
         "download": string | undefined;
         /**
           * The fill for the item. If `"solid"` the item will have a background. If `"outline"` the item will be transparent with a border. Only available in `md` mode.
+          * @deprecated Use the `fill` property on `ion-input` or `ion-textarea` instead.
          */
         "fill"?: 'outline' | 'solid';
         /**
@@ -5407,6 +5408,7 @@ declare namespace LocalJSX {
         "download"?: string | undefined;
         /**
           * The fill for the item. If `"solid"` the item will have a background. If `"outline"` the item will be transparent with a border. Only available in `md` mode.
+          * @deprecated Use the `fill` property on `ion-input` or `ion-textarea` instead.
          */
         "fill"?: 'outline' | 'solid';
         /**

core/src/components/item/item.tsx

@@ -85,6 +85,7 @@ export class Item implements ComponentInterface, AnchorInterface, ButtonInterfac
   /**
    * The fill for the item. If `"solid"` the item will have a background. If
    * `"outline"` the item will be transparent with a border. Only available in `md` mode.
+   * @deprecated Use the `fill` property on `ion-input` or `ion-textarea` instead.
    */
   @Prop() fill?: 'outline' | 'solid';