Layout Grid: Safari issue with background colour and image resizing

@gwwar reported the following issues when testing with Safari:

- The resize handles of an image inside a column disappear after being used once
- The column background colour behaves strange when an image is inside the column

A video can be found in D62390

I've tried to repeat the problem with Safari but everything worked fine, but it's worth investigating further in case it's related to https://github.com/Automattic/block-experiments/pull/197

Start by reviewing the Safari reproduction video in D62390 and the context of pull request 197. Reproduce both reported behaviors in Safari, then determine whether the resize handles and column background color behave correctly when an image is inside a column; done means both issues are fixed and verifiable.

Written by the indexing model from the issue text.