fix(accordion): update styles for ionic theme (#31023)

Issue number: resolves internal

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## What is the current behavior?
There were several issues in the ionic theme which are resolved in this
PR:
- The last item of an accordion had a divider
- The pressed state color did not match design specifications
- Nested accordions did not have not have horizontal padding, causing
the focus state to be different from the parent accordion

## What is the new behavior?
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this PR. -->
The following changes were made in the ionic theme:
- Removed the divider from the final accordion item 
- Update the pressed state color to match design specifications
- Add additional horizontal padding for nested accordion items

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information
- [Basic Accordion
Preview](https://ionic-framework-git-rou-11979-fix-accordian-styles-ionic1.vercel.app/src/components/accordion/test/basic?ionic:theme=ionic)
- [Accordion States
Preview](https://ionic-framework-git-rou-11979-fix-accordian-styles-ionic1.vercel.app/src/components/accordion/test/states?ionic:theme=ionic)
- [Nested Accordion
Preview](https://ionic-framework-git-rou-11979-fix-accordian-styles-ionic1.vercel.app/src/components/accordion/test/nested?ionic:theme=ionic)

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

Author: OS-susmitabhowmik