feat(segment): add default styles for ionic theme (#29897)

Issue number: internal

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## What is the current behavior?
The segment component does not have styles for the `"ionic"` theme and
uses `"md"` styles.

## What is the new behavior?
- Adds styles for both `<ion-segment>` and `<ion-segment-button>` styles
for the `"ionic"` theme
- Adds screenshot tests for the different icon layouts

## Does this introduce a breaking change?

- [ ] Yes
- [x] No