style(segment-button): add and update color to slotted children for improved styling consistency (#30905)

Issue number: resolves internal

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## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->
- Previously in iOS, when using something different than the `ion-label`
to add a text inside the `segment-button`, the default color attributed
to it was blue.
<img width="357" height="103" alt="image"
src="https://github.com/user-attachments/assets/2196e548-f0b7-4e7f-b093-e58c88b2a6cb"
/>

- In Android, the expected color is not attributed either, but it
defaults to black instead of blue.

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->
- Now, all the slotted elements will respect the color defined by the
`color` CSS variable.

## Does this introduce a breaking change?
- [ ] Yes
- [x] No

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## Other information

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screenshots of how the component looks before and after the change. -->