[camera_web] Remove mocktail dependency. (#9195)
Closes https://github.com/flutter/flutter/issues/130757
## Description
- Removes mocktail dependency
- Adds mockito and build_runner dependencies
- Updates tests
## Pre-Review Checklist
[^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.