feat(tab-button): add the shape property and styles for the ionic theme (#30057)

Issue number: internal

---------

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## What is the current behavior?
Tab button does not have a shape property.


## What is the new behavior?
- Adds support for the shape property in tab button.
- Adds styles for the "soft", "round" and "rectangular" shapes in the
ionic theme
- Defaults the shape to "round" for the ionic theme
- Adds an e2e test for shape with screenshots of all shapes


## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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

packages/angular/standalone/src/directives/proxies.ts

@@ -2081,14 +2081,14 @@ export declare interface IonTabBar extends Components.IonTabBar {}
 
 @ProxyCmp({
   defineCustomElementFn: defineIonTabButton,
-  inputs: ['disabled', 'download', 'href', 'layout', 'mode', 'rel', 'selected', 'tab', 'target', 'theme']
+  inputs: ['disabled', 'download', 'href', 'layout', 'mode', 'rel', 'selected', 'shape', 'tab', 'target', 'theme']
 })
 @Component({
   selector: 'ion-tab-button',
   changeDetection: ChangeDetectionStrategy.OnPush,
   template: '<ng-content></ng-content>',
   // eslint-disable-next-line @angular-eslint/no-inputs-metadata-property
-  inputs: ['disabled', 'download', 'href', 'layout', 'mode', 'rel', 'selected', 'tab', 'target', 'theme'],
+  inputs: ['disabled', 'download', 'href', 'layout', 'mode', 'rel', 'selected', 'shape', 'tab', 'target', 'theme'],
   standalone: true
 })
 export class IonTabButton {