Add Console.build_svg() function to get SVG and its size

[jslvtr]

Type of changes

• [ ] Bug fix
• [x] New feature
• [ ] Documentation / docstrings
• [ ] Tests
• [ ] Other

Checklist

• [x] I've run the latest black with default args on new code.
• [x] I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
• [x] I've added tests for new code.
• [x] I accept that @willmcgugan may be pedantic in the code review.

Description

Add Console.build_svg() function to get SVG and its size.

Then changed the existing export_svg() to use the new build_svg() function, but only return the first value which is the SVG string. Power users could then use build_svg() to get the SVG code as well as the width and height.

This is related to issue #2431