better showOffsets

[glaprida]

Aside from the fact that currently showOffsetsSelected is not working ( #4998 ) I have some ideas for a better showOffsets functionality.

It would be great if it could also show the gap property between grid items and flex children as you hover or select the display:grid or display:flex parent.

Also, it would be great if margin-inline:auto (margin-left and margin-right auto) could be displayed as a margin from the element bounds all the way to the parent container.

[artf]

Yeah that would be nice, I think current offset helpers are probably too much hard coded and could be definitely improved to be more customizable. I'd be glad to accept PRs in regards.