Fixed scaling issue with :meth:.BarChart.change_bar_values

[noamzaks]

Changelog / Overview

This closes #1820 by scaling to the height of the bar area instead of the whole VGroup height (which is larger because of the Y-axis at the bottom). It also sets the width and height of the bar area as members so they can be used in future methods.

Fix bug with change_bar_values in :class:~.BarChart

Motivation

The bar chart scales correctly and future methods can use the area of the chart itself.

Testing Status

All tests except test_graphical_units/test_opengl passed on macOS 11

Checklist

• I have read the Contributing Guidelines
• I have written a descriptive PR title (see top of PR template for examples)
• I have written a changelog entry for the PR or deem it unnecessary
• My new functions/classes either have a docstring or are private
• My new functions/classes have tests added and (optional) examples in the docs
• My new documentation builds, looks correctly formatted, and adds no additional build warnings

Reviewer Checklist

• The PR title is descriptive enough
• The PR is labeled correctly
• The changelog entry is completed if necessary
• Newly added functions/classes either have a docstring or are private
• Newly added functions/classes have tests added and (optional) examples in the docs
• Newly added documentation builds, looks correctly formatted, and adds no additional build warnings

[hydrobeam]

This looks good to me, thanks for the contribution!

The current way that bar charts are created is quite convuluted, so when issue #1703 is handled it should hopefully prevent bugs like this 👍