feat(select): add props to customize toggle icons (#27648)

Issue number: resolves #17248

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issue. -->

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## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->

While the `icon` shadow part allows customization of the existing toggle
icon, developers do not have a way to specify a different icon to use
entirely.

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

New props `toggleIcon` and `expandedIcon` added. (Design docs are
[here](https://github.com/ionic-team/ionic-framework-design-documents/blob/main/projects/ionic-framework/components/select/0002-custom-icons.md)
and
[here](https://github.com/ionic-team/ionic-framework-design-documents/blob/main/projects/ionic-framework/components/select/0003-custom-icon-on-open.md)
respectively.)

## 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. -->

Docs PR: https://github.com/ionic-team/ionic-docs/pull/2996
Dev build: `7.0.15-dev.11687278023.161b97d8`

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Co-authored-by: ionitron <hi@ionicframework.com>

packages/vue/src/proxies.ts

@@ -739,6 +739,8 @@ export const IonSelect = /*@__PURE__*/ defineContainer<JSX.IonSelect, JSX.IonSel
   'okText',
   'placeholder',
   'selectedText',
+  'toggleIcon',
+  'expandedIcon',
   'shape',
   'value',
   'ionChange',