rotation paintbrush bug fix

[jilei-hao]

• paintbrush is using pixel index for the update, which is incorrect after rotation
• updating by pixel index will only update the slice in the original (identity transform) space instead of the rotated space

todos

• reference the polygon tool to add drawing based on image coordinates

[jilei-hao]

Todo (updates after 10/23/2023 meeting)

• [x] draw polygon and rasterize to the original segmentation

[jilei-hao]

completed by https://github.com/jilei-hao/itksnap/pull/144