Renamed RollbarCrash interface to RollbarCrashHandler

[matux]

Description of the change

When integrating the SDK as a Framework through SPM, Swift has trouble understanding the difference between the RollbarCrash module and RollbarCrash interface

This PR renames the main RollbarCrash interface from RollbarCrash to RollbarCrashHandler

Type of change

• [x] Bug fix (non-breaking change that fixes an issue)
• [ ] New feature (non-breaking change that adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] Maintenance
• [ ] New release

Related issues

• Attempts to address https://github.com/rollbar/rollbar-apple/issues/328.

Checklists

Development

• [x] Lint rules pass locally
• [x] The code changed/added as part of this pull request has been covered with tests
• [x] All tests related to the changed code pass in development

Code review

• [x] This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• [x] "Ready for review" label attached to the PR and reviewers assigned
• [x] Issue from task tracker has a link to this pull request
• [ ] Changes have been reviewed by at least one other engineer