Paint Bucket Tests

[jordanbrotherton]

Test the paint bucket tool, with a small project and canvas.

on_pointer_down is the only method, but has plenty of tests:

• Test a full screen fill, making sure it terminates properly.
• Test a fill in a contained region, testing tolerances.
• Test edges making sure out of bounds regions are not throwing errors.
• Test if the page is properly updated.

As with the other tests, please refer to the existing tests as an implementation example.