fix(segment): add activated class directly to segment button

[brandyscarney]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Issue Number: N/A

This gets around a bug with Safari where the ::slotted css selector was not working properly

To reproduce, on master:

1. Open the src/components/segment/test/basic?ionic:mode=ios test in Chrome
2. Press down on the checked segment button (with the indicator), see the indicator scale smaller and stays as you drag until you let go
3. Repeat the above in Safari and notice the indicator does not transform until you start dragging and doesn't transform back upon letting go

It may help to visualize it better, the --indicator-transform property can be changed on the segment buttons like --indicator-transform: scale(0.5)

Repeat on this branch, see the scale working properly.

What is the new behavior?

Indicator scales properly on Safari.

Does this introduce a breaking change?

• Yes
• No

Other information