[Calling][Feature] Add ImageButtons for custom buttons

[pavelprystinka]

Purpose

• Add ImageButtons for custom buttons

Does this introduce a breaking change?

• [ ] Yes
• [x] No

Pull Request Type

What kind of change does this Pull Request introduce?

• [ ] Bugfix
• [x] Feature
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Documentation content changes
• [ ] Other... Please describe:

Pull Request Checklist

• [ ] Public API changes
• [ ] Verified for cross-platform
• [ ] Synced with iOS, Web team
• [ ] Internal review completed
• [ ] UI Changes
  • [ ] Screen captures included
  • [ ] Tested for Light/Dark mode
  • [ ] Tested for screen rotation
  • [ ] Tested on Tablet and small screen device (5")
  • [ ] Include localization changes
• [ ] Tests
  • [ ] Memory leak analysis performed
  • [ ] Tested on API 21, 26 and latest
  • [ ] Tested for background mode
  • [ ] Unit Tests Included
  • [ ] UI Automated Tests Included

How to Test

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What to Check

Verify that the following are valid

• ...

Other Information