feat: accordion, improve customizability of toggle icons based on state and add label text

# Feature Request

**Ionic version:**

[ ] **4.x**
[ ] **5.x**
[X] **6.x**

**Describe the Feature Request**

Currently in our App we create a own Accordion Component, which i want to replace by the Ionic one in the Future. But we have two Icons, one for expanded and one for collapsed state, which does not rotate.

I wan't to be able to create it like this too. I can create a PR, but we should discuss the best was to implement this.

**Describe Solutions**

I understand that we can create a own Icon with Class `ion-accordion-toggle-icon` and then no extra Icon will be created. But because of this Class the icon will rotate between the states. So one Option would be to add a `toggleIconRotate: boolean` Prop. I don't like this option as the user has to check by himself if the accordion is collapsed or not and set the specific icon on his own.

**The better option** was if the accordion component would be able to do this itself. So maybe by setting the Type of `toggleIcon` to `string | {collapsed: string; expanded: string;}` and use two different icons based on the state. If this option is used the icon would not rotate.

**Additional Context**

What do you think? Do you prefer a Option? Should i create a PR?

Start at the Ionic accordion component and review the existing ion-accordion-toggle-icon behavior, including how expanded and collapsed states are represented. Clarify whether the desired result is state-specific icons, optional rotation, label text, or all three; done should include the agreed API and coverage for each supported state.

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