fix(backdrop): remove blur effect for ionic theme (#30208)

Issue number internal

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## What is the current behavior?
On the Ionic theme, ion-backdrop has a blur effect whenever it is
visible or hidden.

## What is the new behavior?
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this PR. -->
On the Ionic theme, ion-backdrop no longer has a blur effect regardless
of its state.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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