Add padding to getLabelRotationOffset()

[mikekucera]

Associated issues:

• Rotated label is misplaced when zoomed out #3271

Notes re. the content of the pull request. Give context to reviewers or serve as a general record of the changes made. Add a screenshot or video to demonstrate your new feature, if possible.

• Now when the label rotation offset is calculated it includes the margin/outline/border/padding that is part of the label bounds.
• I don't know if this is the best way to fix the bug. I didn't want to change anything about how the bounding boxes are calculated or saved because I'm concerned I might break something. So instead it saves the "padding" along with the bounding box and uses it when calculating the rotation offset.

Checklist

Author:

• The proper base branch has been selected. New features go on unstable. Bug-fix patches can go on either unstable or master.
• Automated tests have been included in this pull request, if possible, for the new feature(s) or bug fix. Check this box if tests are not pragmatically possible (e.g. rendering features could include screenshots or videos instead of automated tests).
• The associated GitHub issues are included (above).
• Notes have been included (above).

Reviewers:

• All automated checks are passing (green check next to latest commit).
• At least one reviewer has signed off on the pull request.
• For bug fixes: Just after this pull request is merged, it should be applied to both the master branch and the unstable branch. Normally, this just requires cherry-picking the corresponding merge commit from master to unstable -- or vice versa.

[mikekucera]

test_label_position.html.zip

This is the test file I was using. It goes in the root of the project.