Make it possible to remove blocks using tab key in block grid configuration

[bjarnef]

Prerequisites

• I have added steps to test this contribution in the description below

This PR fixes some issues in Block Grid configuration, which was fixed in Block List configuration, but never included in the Block Grid configuration.
Previous PR #12851 fixes issues, where blocks couldn't be removed/deleted using keyboard.

Description

This PR fixes issues deleting/removed blocks from Block Grid configuration using keyboard, which is possible in Block List configuration.

chrome_yhJKsSTNCk.mp4

There is still an issue with focus/outline, when a block as both area and delete button as the outline is on the actions element, so keyboard focus on the two button, but it isn't clear which button has focus.
Should be fixed in another PR.

[github-actions]

Hi there @bjarnef, thank you for this contribution! 👍

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[bjarnef]

It also looks odd how the focus on delete/remove button focus/outline parent container at "Allowed block types" in configuration of area, so I think it may be an issue with how focus/outline works on <umb-button> component.

chrome_VQSwlItGx4.mp4

[mikecp]

Thanks a lot @bjarnef, we'll have a look at it shortly!

[georgebid]

Hey @bjarnef I've tested this one and it's all looking good to me 😄 Therefore, I have merged this in. You should see it in the next release! Thanks again 🥳