Extend mock base chart for mock charts to work

[RasmusKjeldgaard]

What is the new behavior?

Chart Mocks need to extend the BaseChartComponent for the API to match the real implementation.
For now this is a quickfix where I manually extend the already generated MockBaseChartComponent, until #3029 is implemented.

Does this PR introduce a breaking change?

• Yes
• No

Are there any additional context?

Checklist:

The following tasks should be carried out in sequence in order to follow the process of contributing correctly.

Reminders

• Make sure you have implemented tests following the guidelines in: "The good: Test".
• Make sure you have updated the cookbook with examples and showcases (for bug fixes, enhancements & new components).

Review

• Determine if your changes are a fix, feature or breaking-change, and add the matching label to your PR. If it is tooling, dependency updates or similar, add ignore-for-release.
• Do a self-review.
• Request that the changes are code-reviewed
• Request that the changes are UX reviewed (only necessary if your PR introduces visual changes)

When the pull request has been approved it will be merged to develop by Team Kirby.