Indicator in block move mode does not support horizontal layout

[t-hamano]

Description

Originally reported in this comment.

Select Move to from the block toolbar and a blue indicator will appear. This indicator can be manipulated using the arrow keys to know where to move the block.

This indicator is correct when the block is in a vertical layout, but in a horizontal layout such as a Row block, it does not correctly indicate where it is to be inserted.

I think vertical bars should be shown when in a horizontal layout, like when dragging a block from the block inserter.

Step-by-step reproduction instructions

• Insert a paragraph block and a Row block with several blocks.
• Select "Move to" from the Block toolbar for the Paragraph block.
• Use the arrow keys to enter the Row block.
• The indicator should appear as a horizontal bar.

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes